potential memory leak may happen if user space pointer created_timer_id
is invallid. or the value it points to is invalid. the call will
prematurely return.
However it doesn't free the memory it allocates with
alloc_posix_timer(). This patch attempts to fix that by moving parameter
check before alloc_posix_timer().

Reported-by: syzbot+9c47ad18f978d4394986@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69155df4.a70a0220.3124cb.0017.GAE@google.com/T/
Fixes: ec2d0c04624b3 ("posix-timers: Provide a mechanism to allocate a given timer ID")
Suggested-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Eslam Khafagy <eslam.medhat1993@gmail.com>
---
v2:
* Move parameters check before new timer allocation, no need for new
  code.
v1: https://lore.kernel.org/all/20251114050621.875131-1-eslam.medhat1993@gmail.com/T/
---
 kernel/time/posix-timers.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index aa3120104a51..56e17b625c72 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -475,12 +475,6 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
 	if (!kc->timer_create)
 		return -EOPNOTSUPP;
 
-	new_timer = alloc_posix_timer();
-	if (unlikely(!new_timer))
-		return -EAGAIN;
-
-	spin_lock_init(&new_timer->it_lock);
-
 	/* Special case for CRIU to restore timers with a given timer ID. */
 	if (unlikely(current->signal->timer_create_restore_ids)) {
 		if (copy_from_user(&req_id, created_timer_id, sizeof(req_id)))
@@ -490,6 +484,12 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
 			return -EINVAL;
 	}
 
+	new_timer = alloc_posix_timer();
+	if (unlikely(!new_timer))
+		return -EAGAIN;
+
+	spin_lock_init(&new_timer->it_lock);
+
 	/*
 	 * Add the timer to the hash table. The timer is not yet valid
 	 * after insertion, but has a unique ID allocated.
-- 
2.43.0

Le Fri, Nov 14, 2025 at 02:27:39PM +0200, Eslam Khafagy a écrit :
> potential memory leak may happen if user space pointer created_timer_id
> is invallid. or the value it points to is invalid. the call will
> prematurely return.
> However it doesn't free the memory it allocates with
> alloc_posix_timer(). This patch attempts to fix that by moving parameter
> check before alloc_posix_timer().
> 
> Reported-by: syzbot+9c47ad18f978d4394986@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/69155df4.a70a0220.3124cb.0017.GAE@google.com/T/
> Fixes: ec2d0c04624b3 ("posix-timers: Provide a mechanism to allocate a given timer ID")
> Suggested-by: Cyrill Gorcunov <gorcunov@gmail.com>
> Signed-off-by: Eslam Khafagy <eslam.medhat1993@gmail.com>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

-- 
Frederic Weisbecker
SUSE Labs

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     e0fd4d42e27f761e9cc82801b3f183e658dc749d
Gitweb:        https://git.kernel.org/tip/e0fd4d42e27f761e9cc82801b3f183e658dc749d
Author:        Eslam Khafagy <eslam.medhat1993@gmail.com>
AuthorDate:    Fri, 14 Nov 2025 14:27:39 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 14 Nov 2025 16:58:31 +01:00

posix-timers: Plug potential memory leak in do_timer_create()

When posix timer creation is set to allocate a given timer ID and the
access to the user space value faults, the function terminates without
freeing the already allocated posix timer structure.

Move the allocation after the user space access to cure that.

[ tglx: Massaged change log ]

Fixes: ec2d0c04624b3 ("posix-timers: Provide a mechanism to allocate a given timer ID")
Reported-by: syzbot+9c47ad18f978d4394986@syzkaller.appspotmail.com
Suggested-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Eslam Khafagy <eslam.medhat1993@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20251114122739.994326-1-eslam.medhat1993@gmail.com
Closes: https://lore.kernel.org/all/69155df4.a70a0220.3124cb.0017.GAE@google.com/T/
---
 kernel/time/posix-timers.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index aa31201..56e17b6 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -475,12 +475,6 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
 	if (!kc->timer_create)
 		return -EOPNOTSUPP;
 
-	new_timer = alloc_posix_timer();
-	if (unlikely(!new_timer))
-		return -EAGAIN;
-
-	spin_lock_init(&new_timer->it_lock);
-
 	/* Special case for CRIU to restore timers with a given timer ID. */
 	if (unlikely(current->signal->timer_create_restore_ids)) {
 		if (copy_from_user(&req_id, created_timer_id, sizeof(req_id)))
@@ -490,6 +484,12 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
 			return -EINVAL;
 	}
 
+	new_timer = alloc_posix_timer();
+	if (unlikely(!new_timer))
+		return -EAGAIN;
+
+	spin_lock_init(&new_timer->it_lock);
+
 	/*
 	 * Add the timer to the hash table. The timer is not yet valid
 	 * after insertion, but has a unique ID allocated.