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| author | Mickaël Salaün <mic@digikod.net> | 2025-12-19 17:22:59 +0300 |
|---|---|---|
| committer | Mickaël Salaün <mic@digikod.net> | 2025-12-29 18:19:35 +0300 |
| commit | 602acfb541195eb35584d7a3fc7d1db676f059bd (patch) | |
| tree | 924cab5901fe33296d6739c5b96bebd7673b3817 | |
| parent | 6548fb521822a5c0a688e423df28b2248a59543b (diff) | |
| download | linux-602acfb541195eb35584d7a3fc7d1db676f059bd.tar.xz | |
landlock: Optimize stack usage when !CONFIG_AUDIT
Until now, each landlock_request struct were allocated on the stack, even
if not really used, because is_access_to_paths_allowed() unconditionally
modified the passed references. Even if the changed landlock_request
variables are not used, the compiler is not smart enough to detect this
case.
To avoid this issue, explicitly disable the related code when
CONFIG_AUDIT is not set, which enables elision of log_request_parent*
and associated caller's stack variables thanks to dead code elimination.
This makes it possible to reduce the stack frame by 32 bytes for the
path_link and path_rename hooks, and by 20 bytes for most other
filesystem hooks.
Here is a summary of scripts/stackdelta before and after this change
when CONFIG_AUDIT is disabled:
current_check_refer_path 560 320 -240
current_check_access_path 328 184 -144
hook_file_open 328 184 -144
is_access_to_paths_allowed 376 360 -16
Also, add extra pointer checks to be more future-proof.
Cc: Günther Noack <gnoack@google.com>
Reported-by: Tingmao Wang <m@maowtm.org>
Closes: https://lore.kernel.org/r/eb86863b-53b0-460b-b223-84dd31d765b9@maowtm.org
Fixes: 2fc80c69df82 ("landlock: Log file-related denials")
Link: https://lore.kernel.org/r/20251219142302.744917-2-mic@digikod.net
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
[mic: Improve stack usage measurement accuracy with scripts/stackdelta]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
| -rw-r--r-- | security/landlock/fs.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/security/landlock/fs.c b/security/landlock/fs.c index e3c3a8a9ac27..8205673c8b1c 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -939,7 +939,12 @@ jump_up: } path_put(&walker_path); - if (!allowed_parent1) { + /* + * Check CONFIG_AUDIT to enable elision of log_request_parent* and + * associated caller's stack variables thanks to dead code elimination. + */ +#ifdef CONFIG_AUDIT + if (!allowed_parent1 && log_request_parent1) { log_request_parent1->type = LANDLOCK_REQUEST_FS_ACCESS; log_request_parent1->audit.type = LSM_AUDIT_DATA_PATH; log_request_parent1->audit.u.path = *path; @@ -949,7 +954,7 @@ jump_up: ARRAY_SIZE(*layer_masks_parent1); } - if (!allowed_parent2) { + if (!allowed_parent2 && log_request_parent2) { log_request_parent2->type = LANDLOCK_REQUEST_FS_ACCESS; log_request_parent2->audit.type = LSM_AUDIT_DATA_PATH; log_request_parent2->audit.u.path = *path; @@ -958,6 +963,8 @@ jump_up: log_request_parent2->layer_masks_size = ARRAY_SIZE(*layer_masks_parent2); } +#endif /* CONFIG_AUDIT */ + return allowed_parent1 && allowed_parent2; } |