[PATCH] memfd: drop warning for missing exec-related flags

[PATCH] memfd: drop warning for missing exec-related flags

[Aleksa Sarai]

Commit 434ed3350f57 ("memfd: improve userspace warnings for missing
exec-related flags") attempted to make these warnings more useful (so
they would work as an incentive to get users to switch to specifying
these flags -- as intended by the original MFD_NOEXEC_SEAL patchset).
Unfortunately, it turns out that even INFO-level logging is too extreme
to enable by default and alternative solutions to the spam issue (such
as doing more extreme rate-limiting per-task) are either too ugly or
overkill for something as simple as emitting a log as a developer aid.

Given that the flags are new and there is no harm to not specifying them
(after all, we maintain backwards compatibility) we can just drop the
warnings for now until some time in the future when most programs have
migrated and distributions start using vm.memfd_noexec=1 (where failing
to pass the flag would result in unexpected errors for programs that use
executable memfds).

Fixes: 434ed3350f57 ("memfd: improve userspace warnings for missing exec-related flags")
Reported-by: Damian Tometzki <dtometzki@fedoraproject.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 mm/memfd.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index 1cad1904fc26..d3a1ba4208c9 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -315,12 +315,6 @@ SYSCALL_DEFINE2(memfd_create,
 	if ((flags & MFD_EXEC) && (flags & MFD_NOEXEC_SEAL))
 		return -EINVAL;
 
-	if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
-		pr_info_ratelimited(
-			"%s[%d]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set\n",
-			current->comm, task_pid_nr(current));
-	}
-
 	error = check_sysctl_memfd_noexec(&flags);
 	if (error < 0)
 		return error;

---
base-commit: 2374b401b0e0b9ab6d91eead30f9a049f8d620cf
change-id: 20230906-memfd-reduce-spam-8788fc0b951e

Best regards,
-- 
Aleksa Sarai <cyphar@cyphar.com>

Re: [PATCH] memfd: drop warning for missing exec-related flags

[Christian Brauner]

On Wed, Sep 06, 2023 at 05:02:06PM +1000, Aleksa Sarai wrote:
> Commit 434ed3350f57 ("memfd: improve userspace warnings for missing
> exec-related flags") attempted to make these warnings more useful (so
> they would work as an incentive to get users to switch to specifying
> these flags -- as intended by the original MFD_NOEXEC_SEAL patchset).
> Unfortunately, it turns out that even INFO-level logging is too extreme
> to enable by default and alternative solutions to the spam issue (such
> as doing more extreme rate-limiting per-task) are either too ugly or
> overkill for something as simple as emitting a log as a developer aid.
> 
> Given that the flags are new and there is no harm to not specifying them
> (after all, we maintain backwards compatibility) we can just drop the
> warnings for now until some time in the future when most programs have
> migrated and distributions start using vm.memfd_noexec=1 (where failing
> to pass the flag would result in unexpected errors for programs that use
> executable memfds).
> 
> Fixes: 434ed3350f57 ("memfd: improve userspace warnings for missing exec-related flags")
> Reported-by: Damian Tometzki <dtometzki@fedoraproject.org>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---

Looks good to me,
Reviewed-by: Christian Brauner <brauner@kernel.org>

Re: [PATCH] memfd: drop warning for missing exec-related flags

[Andrew Morton]

On Wed, 06 Sep 2023 17:02:06 +1000 Aleksa Sarai <cyphar@cyphar.com> wrote:

> Commit 434ed3350f57 ("memfd: improve userspace warnings for missing
> exec-related flags") attempted to make these warnings more useful (so
> they would work as an incentive to get users to switch to specifying
> these flags -- as intended by the original MFD_NOEXEC_SEAL patchset).
> Unfortunately, it turns out that even INFO-level logging is too extreme
> to enable by default and alternative solutions to the spam issue (such
> as doing more extreme rate-limiting per-task) are either too ugly or
> overkill for something as simple as emitting a log as a developer aid.
> 
> Given that the flags are new and there is no harm to not specifying them
> (after all, we maintain backwards compatibility) we can just drop the
> warnings for now until some time in the future when most programs have
> migrated and distributions start using vm.memfd_noexec=1 (where failing
> to pass the flag would result in unexpected errors for programs that use
> executable memfds).
> 
> Fixes: 434ed3350f57 ("memfd: improve userspace warnings for missing exec-related flags")

This was reverted, so please propose a new patch against 6.6-rc1.