From 8f589c9c3be539d6c2b393c82940c3783831082f Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Mon, 29 Dec 2025 15:38:14 +0000 Subject: rust_binder: correctly handle FDA objects of length zero Fix a bug where an empty FDA (fd array) object with 0 fds would cause an out-of-bounds error. The previous implementation used `skip == 0` to mean "this is a pointer fixup", but 0 is also the correct skip length for an empty FDA. If the FDA is at the end of the buffer, then this results in an attempt to write 8-bytes out of bounds. This is caught and results in an EINVAL error being returned to userspace. The pattern of using `skip == 0` as a special value originates from the C-implementation of Binder. As part of fixing this bug, this pattern is replaced with a Rust enum. I considered the alternate option of not pushing a fixup when the length is zero, but I think it's cleaner to just get rid of the zero-is-special stuff. The root cause of this bug was diagnosed by Gemini CLI on first try. I used the following prompt: > There appears to be a bug in @drivers/android/binder/thread.rs where > the Fixups oob bug is triggered with 316 304 316 324. This implies > that we somehow ended up with a fixup where buffer A has a pointer to > buffer B, but the pointer is located at an index in buffer A that is > out of bounds. Please investigate the code to find the bug. You may > compare with @drivers/android/binder.c that implements this correctly. Cc: stable@vger.kernel.org Reported-by: DeepChirp Closes: https://github.com/waydroid/waydroid/issues/2157 Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver") Tested-by: DeepChirp Signed-off-by: Alice Ryhl Acked-by: Carlos Llamas Link: https://patch.msgid.link/20251229-fda-zero-v1-1-58a41cb0e7ec@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder/thread.rs | 59 +++++++++++++++++++++++----------------- 1 file changed, 34 insertions(+), 25 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binder/thread.rs b/drivers/android/binder/thread.rs index 1a8e6fdc0dc4..dcd47e10aeb8 100644 --- a/drivers/android/binder/thread.rs +++ b/drivers/android/binder/thread.rs @@ -69,17 +69,24 @@ struct ScatterGatherEntry { } /// This entry specifies that a fixup should happen at `target_offset` of the -/// buffer. If `skip` is nonzero, then the fixup is a `binder_fd_array_object` -/// and is applied later. Otherwise if `skip` is zero, then the size of the -/// fixup is `sizeof::()` and `pointer_value` is written to the buffer. -struct PointerFixupEntry { - /// The number of bytes to skip, or zero for a `binder_buffer_object` fixup. - skip: usize, - /// The translated pointer to write when `skip` is zero. - pointer_value: u64, - /// The offset at which the value should be written. The offset is relative - /// to the original buffer. - target_offset: usize, +/// buffer. +enum PointerFixupEntry { + /// A fixup for a `binder_buffer_object`. + Fixup { + /// The translated pointer to write. + pointer_value: u64, + /// The offset at which the value should be written. The offset is relative + /// to the original buffer. + target_offset: usize, + }, + /// A skip for a `binder_fd_array_object`. + Skip { + /// The number of bytes to skip. + skip: usize, + /// The offset at which the skip should happen. The offset is relative + /// to the original buffer. + target_offset: usize, + }, } /// Return type of `apply_and_validate_fixup_in_parent`. @@ -762,8 +769,7 @@ impl Thread { parent_entry.fixup_min_offset = info.new_min_offset; parent_entry.pointer_fixups.push( - PointerFixupEntry { - skip: 0, + PointerFixupEntry::Fixup { pointer_value: buffer_ptr_in_user_space, target_offset: info.target_offset, }, @@ -807,9 +813,8 @@ impl Thread { parent_entry .pointer_fixups .push( - PointerFixupEntry { + PointerFixupEntry::Skip { skip: fds_len, - pointer_value: 0, target_offset: info.target_offset, }, GFP_KERNEL, @@ -871,17 +876,21 @@ impl Thread { let mut reader = UserSlice::new(UserPtr::from_addr(sg_entry.sender_uaddr), sg_entry.length).reader(); for fixup in &mut sg_entry.pointer_fixups { - let fixup_len = if fixup.skip == 0 { - size_of::() - } else { - fixup.skip + let (fixup_len, fixup_offset) = match fixup { + PointerFixupEntry::Fixup { target_offset, .. } => { + (size_of::(), *target_offset) + } + PointerFixupEntry::Skip { + skip, + target_offset, + } => (*skip, *target_offset), }; - let target_offset_end = fixup.target_offset.checked_add(fixup_len).ok_or(EINVAL)?; - if fixup.target_offset < end_of_previous_fixup || offset_end < target_offset_end { + let target_offset_end = fixup_offset.checked_add(fixup_len).ok_or(EINVAL)?; + if fixup_offset < end_of_previous_fixup || offset_end < target_offset_end { pr_warn!( "Fixups oob {} {} {} {}", - fixup.target_offset, + fixup_offset, end_of_previous_fixup, offset_end, target_offset_end @@ -890,13 +899,13 @@ impl Thread { } let copy_off = end_of_previous_fixup; - let copy_len = fixup.target_offset - end_of_previous_fixup; + let copy_len = fixup_offset - end_of_previous_fixup; if let Err(err) = alloc.copy_into(&mut reader, copy_off, copy_len) { pr_warn!("Failed copying into alloc: {:?}", err); return Err(err.into()); } - if fixup.skip == 0 { - let res = alloc.write::(fixup.target_offset, &fixup.pointer_value); + if let PointerFixupEntry::Fixup { pointer_value, .. } = fixup { + let res = alloc.write::(fixup_offset, pointer_value); if let Err(err) = res { pr_warn!("Failed copying ptr into alloc: {:?}", err); return Err(err.into()); -- cgit v1.2.3 From 5e8a3d01544282e50d887d76f30d1496a0a53562 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Thu, 22 Jan 2026 18:02:02 +0000 Subject: binder: fix UAF in binder_netlink_report() Oneway transactions sent to frozen targets via binder_proc_transaction() return a BR_TRANSACTION_PENDING_FROZEN error but they are still treated as successful since the target is expected to thaw at some point. It is then not safe to access 't' after BR_TRANSACTION_PENDING_FROZEN errors as the transaction could have been consumed by the now thawed target. This is the case for binder_netlink_report() which derreferences 't' after a pending frozen error, as pointed out by the following KASAN report: ================================================================== BUG: KASAN: slab-use-after-free in binder_netlink_report.isra.0+0x694/0x6c8 Read of size 8 at addr ffff00000f98ba38 by task binder-util/522 CPU: 4 UID: 0 PID: 522 Comm: binder-util Not tainted 6.19.0-rc6-00015-gc03e9c42ae8f #1 PREEMPT Hardware name: linux,dummy-virt (DT) Call trace: binder_netlink_report.isra.0+0x694/0x6c8 binder_transaction+0x66e4/0x79b8 binder_thread_write+0xab4/0x4440 binder_ioctl+0x1fd4/0x2940 [...] Allocated by task 522: __kmalloc_cache_noprof+0x17c/0x50c binder_transaction+0x584/0x79b8 binder_thread_write+0xab4/0x4440 binder_ioctl+0x1fd4/0x2940 [...] Freed by task 488: kfree+0x1d0/0x420 binder_free_transaction+0x150/0x234 binder_thread_read+0x2d08/0x3ce4 binder_ioctl+0x488/0x2940 [...] ================================================================== Instead, make a transaction copy so the data can be safely accessed by binder_netlink_report() after a pending frozen error. While here, add a comment about not using t->buffer in binder_netlink_report(). Cc: stable@vger.kernel.org Fixes: 63740349eba7 ("binder: introduce transaction reports via netlink") Signed-off-by: Carlos Llamas Reviewed-by: Alice Ryhl Link: https://patch.msgid.link/20260122180203.1502637-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'drivers/android') diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 535fc881c8da..4e16438eceb7 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2991,6 +2991,10 @@ static void binder_set_txn_from_error(struct binder_transaction *t, int id, * @t: the binder transaction that failed * @data_size: the user provided data size for the transaction * @error: enum binder_driver_return_protocol returned to sender + * + * Note that t->buffer is not safe to access here, as it may have been + * released (or not yet allocated). Callers should guarantee all the + * transaction items used here are safe to access. */ static void binder_netlink_report(struct binder_proc *proc, struct binder_transaction *t, @@ -3780,6 +3784,14 @@ static void binder_transaction(struct binder_proc *proc, goto err_dead_proc_or_thread; } } else { + /* + * Make a transaction copy. It is not safe to access 't' after + * binder_proc_transaction() reported a pending frozen. The + * target could thaw and consume the transaction at any point. + * Instead, use a safe 't_copy' for binder_netlink_report(). + */ + struct binder_transaction t_copy = *t; + BUG_ON(target_node == NULL); BUG_ON(t->buffer->async_transaction != 1); return_error = binder_proc_transaction(t, target_proc, NULL); @@ -3790,7 +3802,7 @@ static void binder_transaction(struct binder_proc *proc, */ if (return_error == BR_TRANSACTION_PENDING_FROZEN) { tcomplete->type = BINDER_WORK_TRANSACTION_PENDING; - binder_netlink_report(proc, t, tr->data_size, + binder_netlink_report(proc, &t_copy, tr->data_size, return_error); } binder_enqueue_thread_work(thread, tcomplete); -- cgit v1.2.3 From d047248190d86a52164656d47bec9bfba61dc71e Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Fri, 23 Jan 2026 16:23:56 +0000 Subject: rust_binder: add additional alignment checks This adds some alignment checks to match C Binder more closely. This causes the driver to reject more transactions. I don't think any of the transactions in question are harmful, but it's still a bug because it's the wrong uapi to accept them. The cases where usize is changed for u64, it will affect only 32-bit kernels. Cc: stable@vger.kernel.org Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver") Signed-off-by: Alice Ryhl Acked-by: Carlos Llamas Link: https://patch.msgid.link/20260123-binder-alignment-more-checks-v1-1-7e1cea77411d@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder/thread.rs | 50 +++++++++++++++++++++++++++++----------- 1 file changed, 36 insertions(+), 14 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binder/thread.rs b/drivers/android/binder/thread.rs index dcd47e10aeb8..e0ea33ccfe58 100644 --- a/drivers/android/binder/thread.rs +++ b/drivers/android/binder/thread.rs @@ -39,6 +39,10 @@ use core::{ sync::atomic::{AtomicU32, Ordering}, }; +fn is_aligned(value: usize, to: usize) -> bool { + value % to == 0 +} + /// Stores the layout of the scatter-gather entries. This is used during the `translate_objects` /// call and is discarded when it returns. struct ScatterGatherState { @@ -795,6 +799,10 @@ impl Thread { let num_fds = usize::try_from(obj.num_fds).map_err(|_| EINVAL)?; let fds_len = num_fds.checked_mul(size_of::()).ok_or(EINVAL)?; + if !is_aligned(parent_offset, size_of::()) { + return Err(EINVAL.into()); + } + let info = sg_state.validate_parent_fixup(parent_index, parent_offset, fds_len)?; view.alloc.info_add_fd_reserve(num_fds)?; @@ -809,6 +817,10 @@ impl Thread { } }; + if !is_aligned(parent_entry.sender_uaddr, size_of::()) { + return Err(EINVAL.into()); + } + parent_entry.fixup_min_offset = info.new_min_offset; parent_entry .pointer_fixups @@ -825,6 +837,7 @@ impl Thread { .sender_uaddr .checked_add(parent_offset) .ok_or(EINVAL)?; + let mut fda_bytes = KVec::new(); UserSlice::new(UserPtr::from_addr(fda_uaddr as _), fds_len) .read_all(&mut fda_bytes, GFP_KERNEL)?; @@ -958,25 +971,30 @@ impl Thread { let data_size = trd.data_size.try_into().map_err(|_| EINVAL)?; let aligned_data_size = ptr_align(data_size).ok_or(EINVAL)?; - let offsets_size = trd.offsets_size.try_into().map_err(|_| EINVAL)?; - let aligned_offsets_size = ptr_align(offsets_size).ok_or(EINVAL)?; - let buffers_size = tr.buffers_size.try_into().map_err(|_| EINVAL)?; - let aligned_buffers_size = ptr_align(buffers_size).ok_or(EINVAL)?; + let offsets_size: usize = trd.offsets_size.try_into().map_err(|_| EINVAL)?; + let buffers_size: usize = tr.buffers_size.try_into().map_err(|_| EINVAL)?; let aligned_secctx_size = match secctx.as_ref() { Some((_offset, ctx)) => ptr_align(ctx.len()).ok_or(EINVAL)?, None => 0, }; + if !is_aligned(offsets_size, size_of::()) { + return Err(EINVAL.into()); + } + if !is_aligned(buffers_size, size_of::()) { + return Err(EINVAL.into()); + } + // This guarantees that at least `sizeof(usize)` bytes will be allocated. let len = usize::max( aligned_data_size - .checked_add(aligned_offsets_size) - .and_then(|sum| sum.checked_add(aligned_buffers_size)) + .checked_add(offsets_size) + .and_then(|sum| sum.checked_add(buffers_size)) .and_then(|sum| sum.checked_add(aligned_secctx_size)) .ok_or(ENOMEM)?, - size_of::(), + size_of::(), ); - let secctx_off = aligned_data_size + aligned_offsets_size + aligned_buffers_size; + let secctx_off = aligned_data_size + offsets_size + buffers_size; let mut alloc = match to_process.buffer_alloc(debug_id, len, is_oneway, self.process.task.pid()) { Ok(alloc) => alloc, @@ -1008,13 +1026,13 @@ impl Thread { } let offsets_start = aligned_data_size; - let offsets_end = aligned_data_size + aligned_offsets_size; + let offsets_end = aligned_data_size + offsets_size; // This state is used for BINDER_TYPE_PTR objects. let sg_state = sg_state.insert(ScatterGatherState { unused_buffer_space: UnusedBufferSpace { offset: offsets_end, - limit: len, + limit: offsets_end + buffers_size, }, sg_entries: KVec::new(), ancestors: KVec::new(), @@ -1023,12 +1041,16 @@ impl Thread { // Traverse the objects specified. let mut view = AllocationView::new(&mut alloc, data_size); for (index, index_offset) in (offsets_start..offsets_end) - .step_by(size_of::()) + .step_by(size_of::()) .enumerate() { - let offset = view.alloc.read(index_offset)?; + let offset: usize = view + .alloc + .read::(index_offset)? + .try_into() + .map_err(|_| EINVAL)?; - if offset < end_of_previous_object { + if offset < end_of_previous_object || !is_aligned(offset, size_of::()) { pr_warn!("Got transaction with invalid offset."); return Err(EINVAL.into()); } @@ -1060,7 +1082,7 @@ impl Thread { } // Update the indexes containing objects to clean up. - let offset_after_object = index_offset + size_of::(); + let offset_after_object = index_offset + size_of::(); view.alloc .set_info_offsets(offsets_start..offset_after_object); } -- cgit v1.2.3 From 1769f90e5ba2a6d24bb46b85da33fe861c68f005 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Fri, 23 Jan 2026 17:57:02 +0000 Subject: binder: fix BR_FROZEN_REPLY error log The error logging for failed transactions is misleading as it always reports "dead process or thread" even when the target is actually frozen. Additionally, the pid and tid are reversed which can further confuse debugging efforts. Fix both issues. Cc: stable@kernel.org Cc: Steven Moreland Fixes: a15dac8b2286 ("binder: additional transaction error logs") Signed-off-by: Carlos Llamas Reviewed-by: Alice Ryhl Link: https://patch.msgid.link/20260123175702.2154348-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 4e16438eceb7..b356c9b88254 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -3824,8 +3824,9 @@ static void binder_transaction(struct binder_proc *proc, return; err_dead_proc_or_thread: - binder_txn_error("%d:%d dead process or thread\n", - thread->pid, proc->pid); + binder_txn_error("%d:%d %s process or thread\n", + proc->pid, thread->pid, + return_error == BR_FROZEN_REPLY ? "frozen" : "dead"); return_error_line = __LINE__; binder_dequeue_work(proc, tcomplete); err_translate_failed: -- cgit v1.2.3 From d6ba734814266bbf7ee01f9030436597116805f3 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Tue, 27 Jan 2026 23:55:10 +0000 Subject: rust_binderfs: fix ida_alloc_max() upper bound The 'max' argument of ida_alloc_max() takes the maximum valid ID and not the "count". Using an ID of BINDERFS_MAX_MINOR (1 << 20) for dev->minor would exceed the limits of minor numbers (20-bits). Fix this off-by-one error by subtracting 1 from the 'max'. Cc: stable@vger.kernel.org Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver") Reported-by: kernel test robot Closes: https://lore.kernel.org/r/202512181203.IOv6IChH-lkp@intel.com/ Signed-off-by: Carlos Llamas Reviewed-by: Alice Ryhl Link: https://patch.msgid.link/20260127235545.2307876-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder/rust_binderfs.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binder/rust_binderfs.c b/drivers/android/binder/rust_binderfs.c index c69026df775c..88374b31ab7c 100644 --- a/drivers/android/binder/rust_binderfs.c +++ b/drivers/android/binder/rust_binderfs.c @@ -132,8 +132,8 @@ static int binderfs_binder_device_create(struct inode *ref_inode, mutex_lock(&binderfs_minors_mutex); if (++info->device_count <= info->mount_opts.max) minor = ida_alloc_max(&binderfs_minors, - use_reserve ? BINDERFS_MAX_MINOR : - BINDERFS_MAX_MINOR_CAPPED, + use_reserve ? BINDERFS_MAX_MINOR - 1 : + BINDERFS_MAX_MINOR_CAPPED - 1, GFP_KERNEL); else minor = -ENOSPC; @@ -405,8 +405,8 @@ static int binderfs_binder_ctl_create(struct super_block *sb) /* Reserve a new minor number for the new device. */ mutex_lock(&binderfs_minors_mutex); minor = ida_alloc_max(&binderfs_minors, - use_reserve ? BINDERFS_MAX_MINOR : - BINDERFS_MAX_MINOR_CAPPED, + use_reserve ? BINDERFS_MAX_MINOR - 1 : + BINDERFS_MAX_MINOR_CAPPED - 1, GFP_KERNEL); mutex_unlock(&binderfs_minors_mutex); if (minor < 0) { -- cgit v1.2.3 From ec4ddc90d201d09ef4e4bef8a2c6d9624525ad68 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Tue, 27 Jan 2026 23:55:11 +0000 Subject: binderfs: fix ida_alloc_max() upper bound The 'max' argument of ida_alloc_max() takes the maximum valid ID and not the "count". Using an ID of BINDERFS_MAX_MINOR (1 << 20) for dev->minor would exceed the limits of minor numbers (20-bits). Fix this off-by-one error by subtracting 1 from the 'max'. Cc: stable@vger.kernel.org Fixes: 3ad20fe393b3 ("binder: implement binderfs") Signed-off-by: Carlos Llamas Link: https://patch.msgid.link/20260127235545.2307876-2-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binderfs.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c index b46bcb91072d..9f8a18c88d66 100644 --- a/drivers/android/binderfs.c +++ b/drivers/android/binderfs.c @@ -132,8 +132,8 @@ static int binderfs_binder_device_create(struct inode *ref_inode, mutex_lock(&binderfs_minors_mutex); if (++info->device_count <= info->mount_opts.max) minor = ida_alloc_max(&binderfs_minors, - use_reserve ? BINDERFS_MAX_MINOR : - BINDERFS_MAX_MINOR_CAPPED, + use_reserve ? BINDERFS_MAX_MINOR - 1 : + BINDERFS_MAX_MINOR_CAPPED - 1, GFP_KERNEL); else minor = -ENOSPC; @@ -408,8 +408,8 @@ static int binderfs_binder_ctl_create(struct super_block *sb) /* Reserve a new minor number for the new device. */ mutex_lock(&binderfs_minors_mutex); minor = ida_alloc_max(&binderfs_minors, - use_reserve ? BINDERFS_MAX_MINOR : - BINDERFS_MAX_MINOR_CAPPED, + use_reserve ? BINDERFS_MAX_MINOR - 1 : + BINDERFS_MAX_MINOR_CAPPED - 1, GFP_KERNEL); mutex_unlock(&binderfs_minors_mutex); if (minor < 0) { -- cgit v1.2.3