From b5782e2d462c028096f922abca46318cec890670 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 12 May 2026 13:33:40 +0100 Subject: netfs: Fix missing barriers when accessing stream->subrequests locklessly The list of subrequests attached to stream->subrequests is accessed without locks by netfs_collect_read_results() and netfs_collect_write_results(), and then they access subreq->flags without taking a barrier after getting the subreq pointer from the list. Relatedly, the functions that build the list don't use any sort of write barrier when constructing the list to make sure that the NETFS_SREQ_IN_PROGRESS flag is perceived to be set first if no lock is taken. Fix this by: (1) Add a new list_add_tail_release() function that uses a release barrier to set the pointer to the new member of the list. (2) Add a new list_first_entry_or_null_acquire() function that uses an acquire barrier to read the pointer to the first member in a list (or return NULL). (3) Use list_add_tail_release() when adding a subreq to ->subrequests. (4) Use list_first_entry_or_null_acquire() when initially accessing the front of the list (when an item is removed, the pointer to the new front iterm is obtained under the same lock). Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Link: https://sashiko.dev/#/patchset/20260326104544.509518-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-4-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- include/linux/list.h | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'include/linux') diff --git a/include/linux/list.h b/include/linux/list.h index 00ea8e5fb88b..09d979976b3b 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -191,6 +191,29 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head) __list_add(new, head->prev, head); } +/** + * list_add_tail_release - add a new entry with release barrier + * @new: new entry to be added + * @head: list head to add it before + * + * Insert a new entry before the specified head, using a release barrier to set + * the ->next pointer that points to it. This is useful for implementing + * queues, in particular one that the elements will be walked through forwards + * locklessly. + */ +static inline void list_add_tail_release(struct list_head *new, + struct list_head *head) +{ + struct list_head *prev = head->prev; + + if (__list_add_valid(new, prev, head)) { + new->next = head; + new->prev = prev; + head->prev = new; + smp_store_release(&prev->next, new); + } +} + /* * Delete a list entry by making the prev/next entries * point to each other. @@ -644,6 +667,20 @@ static inline void list_splice_tail_init(struct list_head *list, pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ }) +/** + * list_first_entry_or_null_acquire - get the first element from a list with barrier + * @ptr: the list head to take the element from. + * @type: the type of the struct this is embedded in. + * @member: the name of the list_head within the struct. + * + * Note that if the list is empty, it returns NULL. + */ +#define list_first_entry_or_null_acquire(ptr, type, member) ({ \ + struct list_head *head__ = (ptr); \ + struct list_head *pos__ = smp_load_acquire(&head__->next); \ + pos__ != head__ ? list_entry(pos__, type, member) : NULL; \ +}) + /** * list_last_entry_or_null - get the last element from a list * @ptr: the list head to take the element from. -- cgit v1.2.3 From 2c8f4742bb76117d735f92a3932d85239b16c494 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 12 May 2026 13:33:42 +0100 Subject: netfs: Fix potential for tearing in ->remote_i_size and ->zero_point Fix potential tearing in using ->remote_i_size and ->zero_point by copying i_size_read() and i_size_write() and using the same seqcount as for i_size. We need to make sure that netfslib and the filesystems that use it always hold i_lock whilst updating any of the sizes to prevent i_size_seqcount from getting corrupted. Fixes: 4058f742105e ("netfs: Keep track of the actual remote file size") Fixes: 100ccd18bb41 ("netfs: Optimise away reads above the point at which there can be no data") Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-6-dhowells@redhat.com cc: Paulo Alcantara cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- include/linux/netfs.h | 293 ++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 284 insertions(+), 9 deletions(-) (limited to 'include/linux') diff --git a/include/linux/netfs.h b/include/linux/netfs.h index ba17ac5bf356..4fd1d796ad73 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -62,8 +62,8 @@ struct netfs_inode { struct fscache_cookie *cache; #endif struct mutex wb_lock; /* Writeback serialisation */ - loff_t remote_i_size; /* Size of the remote file */ - loff_t zero_point; /* Size after which we assume there's no data + loff_t _remote_i_size; /* Size of the remote file */ + loff_t _zero_point; /* Size after which we assume there's no data * on the server */ atomic_t io_count; /* Number of outstanding reqs */ unsigned long flags; @@ -474,6 +474,254 @@ static inline struct netfs_inode *netfs_inode(struct inode *inode) return container_of(inode, struct netfs_inode, inode); } +/** + * netfs_read_remote_i_size - Read remote_i_size safely + * @inode: The inode to access + * + * Read remote_i_size safely without the potential for tearing on 32-bit + * arches. + * + * NOTE: in a 32bit arch with a preemptable kernel and an UP compile the + * i_size_read/write must be atomic with respect to the local cpu (unlike with + * preempt disabled), but they don't need to be atomic with respect to other + * cpus like in true SMP (so they need either to either locally disable irq + * around the read or for example on x86 they can be still implemented as a + * cmpxchg8b without the need of the lock prefix). For SMP compiles and 64bit + * archs it makes no difference if preempt is enabled or not. + */ +static inline unsigned long long netfs_read_remote_i_size(const struct inode *inode) +{ + const struct netfs_inode *ictx = container_of(inode, struct netfs_inode, inode); + unsigned long long remote_i_size; + +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + unsigned int seq; + + do { + seq = read_seqcount_begin(&inode->i_size_seqcount); + remote_i_size = ictx->_remote_i_size; + } while (read_seqcount_retry(&inode->i_size_seqcount, seq)); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + remote_i_size = ictx->_remote_i_size; + preempt_enable(); +#else + /* Pairs with smp_store_release() in netfs_write_remote_i_size() */ + remote_i_size = smp_load_acquire(&ictx->_remote_i_size); +#endif + return remote_i_size; +} + +/* + * netfs_write_remote_i_size - Set remote_i_size safely + * @inode: The inode to access + * @remote_i_size: The new value for the size of the file on the server + * + * Set remote_i_size safely without the potential for tearing on 32-bit arches. + * + * Context: The caller must hold inode->i_lock. + * + * NOTE: unlike netfs_read_remote_i_size(), netfs_write_remote_i_size() does + * need locking around it (normally i_rwsem), otherwise on 32bit/SMP an update + * of i_size_seqcount can be lost, resulting in subsequent i_size_read() calls + * spinning forever. + */ +static inline void netfs_write_remote_i_size(struct inode *inode, + unsigned long long remote_i_size) +{ + struct netfs_inode *ictx = netfs_inode(inode); + +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + write_seqcount_begin(&inode->i_size_seqcount); + ictx->_remote_i_size = remote_i_size; + write_seqcount_end(&inode->i_size_seqcount); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + ictx->_remote_i_size = remote_i_size; + preempt_enable(); +#else + /* + * Pairs with smp_load_acquire() in netfs_read_remote_i_size() to + * ensure changes related to inode size (such as page contents) are + * visible before we see the changed inode size. + */ + smp_store_release(&ictx->_remote_i_size, remote_i_size); +#endif +} + +/** + * netfs_read_zero_point - Read zero_point safely + * @inode: The inode to access + * + * Read zero_point safely without the potential for tearing on 32-bit + * arches. + * + * NOTE: in a 32bit arch with a preemptable kernel and an UP compile the + * i_size_read/write must be atomic with respect to the local cpu (unlike with + * preempt disabled), but they don't need to be atomic with respect to other + * cpus like in true SMP (so they need either to either locally disable irq + * around the read or for example on x86 they can be still implemented as a + * cmpxchg8b without the need of the lock prefix). For SMP compiles and 64bit + * archs it makes no difference if preempt is enabled or not. + */ +static inline unsigned long long netfs_read_zero_point(const struct inode *inode) +{ + struct netfs_inode *ictx = container_of(inode, struct netfs_inode, inode); + unsigned long long zero_point; + +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + unsigned int seq; + + do { + seq = read_seqcount_begin(&inode->i_size_seqcount); + zero_point = ictx->_zero_point; + } while (read_seqcount_retry(&inode->i_size_seqcount, seq)); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + zero_point = ictx->_zero_point; + preempt_enable(); +#else + /* Pairs with smp_store_release() in netfs_write_zero_point() */ + zero_point = smp_load_acquire(&ictx->_zero_point); +#endif + return zero_point; +} + +/* + * netfs_write_zero_point - Set zero_point safely + * @inode: The inode to access + * @zero_point: The new value for the point beyond which the server has no data + * + * Set zero_point safely without the potential for tearing on 32-bit arches. + * + * Context: The caller must hold inode->i_lock. + * + * NOTE: unlike netfs_read_zero_point(), netfs_write_zero_point() does need + * locking around it (normally i_rwsem), otherwise on 32bit/SMP an update of + * i_size_seqcount can be lost, resulting in subsequent read calls spinning + * forever. + */ +static inline void netfs_write_zero_point(struct inode *inode, + unsigned long long zero_point) +{ + struct netfs_inode *ictx = netfs_inode(inode); + +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + write_seqcount_begin(&inode->i_size_seqcount); + ictx->_zero_point = zero_point; + write_seqcount_end(&inode->i_size_seqcount); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + ictx->_zero_point = zero_point; + preempt_enable(); +#else + /* + * Pairs with smp_load_acquire() in netfs_read_zero_point() to + * ensure changes related to inode size (such as page contents) are + * visible before we see the changed inode size. + */ + smp_store_release(&ictx->_zero_point, zero_point); +#endif +} + +/** + * netfs_read_sizes - Read remote_i_size and zero_point safely + * @inode: The inode to access + * @i_size: Where to return the local file size. + * @remote_i_size: Where to return the size of the file on the server + * @zero_point: Where to return the the point beyond which the server has no data + * + * Read remote_i_size and zero_point safely without the potential for tearing + * on 32-bit arches. + * + * NOTE: in a 32bit arch with a preemptable kernel and an UP compile the + * i_size_read/write must be atomic with respect to the local cpu (unlike with + * preempt disabled), but they don't need to be atomic with respect to other + * cpus like in true SMP (so they need either to either locally disable irq + * around the read or for example on x86 they can be still implemented as a + * cmpxchg8b without the need of the lock prefix). For SMP compiles and 64bit + * archs it makes no difference if preempt is enabled or not. + */ +static inline void netfs_read_sizes(const struct inode *inode, + unsigned long long *i_size, + unsigned long long *remote_i_size, + unsigned long long *zero_point) +{ + const struct netfs_inode *ictx = container_of(inode, struct netfs_inode, inode); +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + unsigned int seq; + + do { + seq = read_seqcount_begin(&inode->i_size_seqcount); + *i_size = inode->i_size; + *remote_i_size = ictx->_remote_i_size; + *zero_point = ictx->_zero_point; + } while (read_seqcount_retry(&inode->i_size_seqcount, seq)); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + *i_size = inode->i_size; + *remote_i_size = ictx->_remote_i_size; + *zero_point = ictx->_zero_point; + preempt_enable(); +#else + /* Pairs with smp_store_release() in i_size_write() */ + *i_size = smp_load_acquire(&inode->i_size); + /* Pairs with smp_store_release() in netfs_write_remote_i_size() */ + *remote_i_size = smp_load_acquire(&ictx->_remote_i_size); + /* Pairs with smp_store_release() in netfs_write_zero_point() */ + *zero_point = smp_load_acquire(&ictx->_zero_point); +#endif +} + +/* + * netfs_write_sizes - Set i_size, remote_i_size and zero_point safely + * @inode: The inode to access + * @i_size: The new value for the local size of the file + * @remote_i_size: The new value for the size of the file on the server + * @zero_point: The new value for the point beyond which the server has no data + * + * Set both remote_i_size and zero_point safely without the potential for + * tearing on 32-bit arches. + * + * Context: The caller must hold inode->i_lock. + * + * NOTE: unlike netfs_read_zero_point(), netfs_write_zero_point() does need + * locking around it (normally i_rwsem), otherwise on 32bit/SMP an update of + * i_size_seqcount can be lost, resulting in subsequent read calls spinning + * forever. + */ +static inline void netfs_write_sizes(struct inode *inode, + unsigned long long i_size, + unsigned long long remote_i_size, + unsigned long long zero_point) +{ + struct netfs_inode *ictx = netfs_inode(inode); + +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + write_seqcount_begin(&inode->i_size_seqcount); + inode->i_size = i_size; + ictx->_remote_i_size = remote_i_size; + ictx->_zero_point = zero_point; + write_seqcount_end(&inode->i_size_seqcount); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + inode->i_size = i_size; + ictx->_remote_i_size = remote_i_size; + ictx->_zero_point = zero_point; + preempt_enable(); +#else + /* + * Pairs with smp_load_acquire() in i_size_read(), + * netfs_read_remote_i_size() and netfs_read_zero_point() to ensure + * changes related to inode size (such as page contents) are visible + * before we see the changed inode size. + */ + smp_store_release(&inode->i_size, i_size); + smp_store_release(&ictx->_remote_i_size, remote_i_size); + smp_store_release(&ictx->_zero_point, zero_point); +#endif +} + /** * netfs_inode_init - Initialise a netfslib inode context * @ctx: The netfs inode to initialise @@ -488,8 +736,8 @@ static inline void netfs_inode_init(struct netfs_inode *ctx, bool use_zero_point) { ctx->ops = ops; - ctx->remote_i_size = i_size_read(&ctx->inode); - ctx->zero_point = LLONG_MAX; + ctx->_remote_i_size = i_size_read(&ctx->inode); + ctx->_zero_point = LLONG_MAX; ctx->flags = 0; atomic_set(&ctx->io_count, 0); #if IS_ENABLED(CONFIG_FSCACHE) @@ -498,7 +746,7 @@ static inline void netfs_inode_init(struct netfs_inode *ctx, mutex_init(&ctx->wb_lock); /* ->releasepage() drives zero_point */ if (use_zero_point) { - ctx->zero_point = ctx->remote_i_size; + ctx->_zero_point = ctx->_remote_i_size; mapping_set_release_always(ctx->inode.i_mapping); } } @@ -511,13 +759,40 @@ static inline void netfs_inode_init(struct netfs_inode *ctx, * * Inform the netfs lib that a file got resized so that it can adjust its state. */ -static inline void netfs_resize_file(struct netfs_inode *ctx, loff_t new_i_size, +static inline void netfs_resize_file(struct netfs_inode *ictx, + unsigned long long new_i_size, bool changed_on_server) { +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + struct inode *inode = &ictx->inode; + + preempt_disable(); + write_seqcount_begin(&inode->i_size_seqcount); + if (changed_on_server) + ictx->_remote_i_size = new_i_size; + if (new_i_size < ictx->_zero_point) + ictx->_zero_point = new_i_size; + write_seqcount_end(&inode->i_size_seqcount); + preempt_enable(); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); if (changed_on_server) - ctx->remote_i_size = new_i_size; - if (new_i_size < ctx->zero_point) - ctx->zero_point = new_i_size; + ictx->_remote_i_size = new_i_size; + if (new_i_size < ictx->_zero_point) + ictx->_zero_point = new_i_size; + preempt_enable(); +#else + /* + * Pairs with smp_load_acquire() in netfs_read_remote_i_size and + * netfs_read_zero_point() to ensure changes related to inode size + * (such as page contents) are visible before we see the changed inode + * size. + */ + if (changed_on_server) + smp_store_release(&ictx->_remote_i_size, new_i_size); + if (new_i_size < ictx->_zero_point) + smp_store_release(&ictx->_zero_point, new_i_size); +#endif } /** -- cgit v1.2.3 From dbe556972100fabb8e5a1b3d2163831ff07b1e8e Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 12 May 2026 13:33:56 +0100 Subject: netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it is wanting to unlock and compares that to rreq->no_unlock_folio so that it doesn't unlock a folio being read for netfs_perform_write() or netfs_write_begin(). However, given that netfs_unlock_abandoned_read_pages() is called _after_ NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to dereference is the one specified by ->no_unlock_folio as ownership immediately reverts to the caller. Fix this by storing the folio pointer instead and using that rather than the index. Also fix netfs_unlock_read_folio() where the same applies. Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading") Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-20-dhowells@redhat.com cc: Paulo Alcantara cc: Viacheslav Dubeyko cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- include/linux/netfs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/netfs.h b/include/linux/netfs.h index 4fd1d796ad73..243c0f737938 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -252,7 +252,7 @@ struct netfs_io_request { unsigned long long collected_to; /* Point we've collected to */ unsigned long long cleaned_to; /* Position we've cleaned folios to */ unsigned long long abandon_to; /* Position to abandon folios to */ - pgoff_t no_unlock_folio; /* Don't unlock this folio after read */ + const struct folio *no_unlock_folio; /* Don't unlock this folio after read */ unsigned int direct_bv_count; /* Number of elements in direct_bv[] */ unsigned int debug_id; unsigned int rsize; /* Maximum read size (0 for none) */ -- cgit v1.2.3