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authorGünther Noack <gnoack3000@gmail.com>2022-10-18 20:22:09 +0200
committerMickaël Salaün <mic@digikod.net>2022-10-19 09:01:44 +0200
commitb9f5ce27c8f8be409d6afca9797a2da01e5cebbb (patch)
tree6b732e7cdba7f9241fc131784a438a09f2b0b162 /security/security.c
parent52a13488d1783ae014a3abe15f78810162425e94 (diff)
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landlock: Support file truncation
Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. This flag hooks into the path_truncate, file_truncate and file_alloc_security LSM hooks and covers file truncation using truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat(). This change also increments the Landlock ABI version, updates corresponding selftests, and updates code documentation to document the flag. In security/security.c, allocate security blobs at pointer-aligned offsets. This fixes the problem where one LSM's security blob can shift another LSM's security blob to an unaligned address (reported by Nathan Chancellor). The following operations are restricted: open(2): requires the LANDLOCK_ACCESS_FS_TRUNCATE right if a file gets implicitly truncated as part of the open() (e.g. using O_TRUNC). Notable special cases: * open(..., O_RDONLY|O_TRUNC) can truncate files as well in Linux * open() with O_TRUNC does *not* need the TRUNCATE right when it creates a new file. truncate(2) (on a path): requires the LANDLOCK_ACCESS_FS_TRUNCATE right. ftruncate(2) (on a file): requires that the file had the TRUNCATE right when it was previously opened. File descriptors acquired by other means than open(2) (e.g. memfd_create(2)) continue to support truncation with ftruncate(2). Cc: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Günther Noack <gnoack3000@gmail.com> Acked-by: Paul Moore <paul@paul-moore.com> (LSM) Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com Signed-off-by: Mickaël Salaün <mic@digikod.net>
Diffstat (limited to 'security/security.c')
-rw-r--r--security/security.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/security/security.c b/security/security.c
index b55596958d0c..e0fe4ba39eb9 100644
--- a/security/security.c
+++ b/security/security.c
@@ -185,11 +185,12 @@ static void __init lsm_set_blob_size(int *need, int *lbs)
{
int offset;
- if (*need > 0) {
- offset = *lbs;
- *lbs += *need;
- *need = offset;
- }
+ if (*need <= 0)
+ return;
+
+ offset = ALIGN(*lbs, sizeof(void *));
+ *lbs = offset + *need;
+ *need = offset;
}
static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)