If a recursive call to ep_loop_check_proc() hits the `result = INT_MAX`,
an integer overflow will occur in the calling ep_loop_check_proc() at
`result = max(result, ep_loop_check_proc(ep_tovisit, depth + 1) + 1)`,
breaking the recursion depth check.

Fix it by using a different placeholder value that can't lead to an
overflow.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes: f2e467a48287 ("eventpoll: Fix semi-unbounded recursion")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
---
Gah, I introduced such an obvious integer overflow when I touched this
code the last time...

No "Closes:" link because the bug was not reported publicly.
---
 fs/eventpoll.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index a8c278c50083..5714e900567c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2061,7 +2061,8 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
  * @ep: the &struct eventpoll to be currently checked.
  * @depth: Current depth of the path being checked.
  *
- * Return: depth of the subtree, or INT_MAX if we found a loop or went too deep.
+ * Return: depth of the subtree, or a value bigger than EP_MAX_NESTS if we found
+ * a loop or went too deep.
  */
 static int ep_loop_check_proc(struct eventpoll *ep, int depth)
 {
@@ -2080,7 +2081,7 @@ static int ep_loop_check_proc(struct eventpoll *ep, int depth)
 			struct eventpoll *ep_tovisit;
 			ep_tovisit = epi->ffd.file->private_data;
 			if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS)
-				result = INT_MAX;
+				result = EP_MAX_NESTS+1;
 			else
 				result = max(result, ep_loop_check_proc(ep_tovisit, depth + 1) + 1);
 			if (result > EP_MAX_NESTS)

---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260223-epoll-int-overflow-3a04bf73eca6

--  
Jann Horn <jannh@google.com>

On Mon, 23 Feb 2026 20:59:33 +0100, Jann Horn wrote:
> If a recursive call to ep_loop_check_proc() hits the `result = INT_MAX`,
> an integer overflow will occur in the calling ep_loop_check_proc() at
> `result = max(result, ep_loop_check_proc(ep_tovisit, depth + 1) + 1)`,
> breaking the recursion depth check.
> 
> Fix it by using a different placeholder value that can't lead to an
> overflow.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] eventpoll: Fix integer overflow in ep_loop_check_proc()
      https://git.kernel.org/vfs/vfs/c/fdcfce93073d