Nicholas reported that his LLM found it was possible to create a UaF
when sys_futex_requeue() is used with different flags. The initial
motivation for allowing different flags was the variable sized futex,
but since that hasn't been merged (yet), simply mandate the flags are
identical, as is the case for the old style sys_futex() requeue
operations.

Fixes: 0f4b5f972216 ("futex: Add sys_futex_requeue()")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

This was done entirely with mindless brute force, using

    git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
        xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'

to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.

Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.

For the same reason the 'flex' versions will be done as a separate
conversion.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:

Single allocations:	kmalloc(sizeof(TYPE), ...)
are replaced with:	kmalloc_obj(TYPE, ...)

Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with:	kmalloc_objs(TYPE, COUNT, ...)

Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)

(where TYPE may also be *VAR)

The resulting allocations no longer return "void *", instead returning
"TYPE *".

Signed-off-by: Kees Cook <kees@kernel.org>

sys_get_robust_list() and compat_get_robust_list() use ptrace_may_access()
to check if the calling task is allowed to access another task's
robust_list pointer. This check is racy against a concurrent exec() in the
target process.

During exec(), a task may transition from a non-privileged binary to a
privileged one (e.g., setuid binary) and its credentials/memory mappings
may change. If get_robust_list() performs ptrace_may_access() before
this transition, it may erroneously allow access to sensitive information
after the target becomes privileged.

A racy access allows an attacker to exploit a window during which
ptrace_may_access() passes before a target process transitions to a
privileged state via exec().

For example, consider a non-privileged task T that is about to execute a
setuid-root binary. An attacker task A calls get_robust_list(T) while T
is still unprivileged. Since ptrace_may_access() checks permissions
based on current credentials, it succeeds. However, if T begins exec
immediately afterwards, it becomes privileged and may change its memory
mappings. Because get_robust_list() proceeds to access T->robust_list
without synchronizing with exec() it may read user-space pointers from a
now-privileged process.

This violates the intended post-exec access restrictions and could
expose sensitive memory addresses or be used as a primitive in a larger
exploit chain. Consequently, the race can lead to unauthorized
disclosure of information across privilege boundaries and poses a
potential security risk.

Take a read lock on signal->exec_update_lock prior to invoking
ptrace_may_access() and accessing the robust_list/compat_robust_list.
This ensures that the target task's exec state remains stable during the
check, allowing for consistent and synchronized validation of
credentials.

Suggested-by: Jann Horn <jann@thejh.net>
Signed-off-by: Pranav Tyagi <pranav.tyagi03@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/linux-fsdevel/1477863998-3298-5-git-send-email-jann@thejh.net/
Link: https://github.com/KSPP/linux/issues/119

To make it more generically useful, augment it with allowing the caller
to pass in the wake handler and wake data. Convert the futex_waitv()
syscall, passing in the default handlers.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We need this for validating the futex2 flags outside of the normal
futex syscalls.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Finish off the 'simple' futex2 syscall group by adding
sys_futex_requeue(). Unlike sys_futex_{wait,wake}() its arguments are
too numerous to fit into a regular syscall. As such, use struct
futex_waitv to pass the 'source' and 'destination' futexes to the
syscall.

This syscall implements what was previously known as FUTEX_CMP_REQUEUE
and uses {val, uaddr, flags} for source and {uaddr, flags} for
destination.

This design explicitly allows requeueing between different types of
futex by having a different flags word per uaddr.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230921105248.511860556@noisy.programming.kicks-ass.net

In order to support mixed size requeue, add a second flags argument to
the internal futex_requeue() function.

No functional change intended.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105248.396780136@noisy.programming.kicks-ass.net

To complement sys_futex_waitv()/wake(), add sys_futex_wait(). This
syscall implements what was previously known as FUTEX_WAIT_BITSET
except it uses 'unsigned long' for the value and bitmask arguments,
takes timespec and clockid_t arguments for the absolute timeout and
uses FUTEX2 flags.

The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230921105248.164324363@noisy.programming.kicks-ass.net

The current semantics for futex_wake() are a bit loose, specifically
asking for 0 futexes to be woken actually gets you 1.

Adding a !nr check to sys_futex_wake() makes that it would return 0
for unaligned futex words, because that check comes in the shared
futex_wake() function. Adding the !nr check there, would affect the
legacy sys_futex() semantics.

Hence frob a flag :-(

Suggested-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105248.048643656@noisy.programming.kicks-ass.net