From b9f5ce27c8f8be409d6afca9797a2da01e5cebbb Mon Sep 17 00:00:00 2001 From: Günther Noack Date: Tue, 18 Oct 2022 20:22:09 +0200 Subject: landlock: Support file truncation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Günther Noack Acked-by: Paul Moore (LSM) Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com Signed-off-by: Mickaël Salaün --- security/security.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'security/security.c') 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) -- cgit v1.2.3