From: Ondrej Mosnacek omosnace@redhat.com
[ Upstream commit e7eda157c4071cd1e69f4b1687b0fbe1ae5e6f46 ]
The check being unconditional may lead to unwanted denials reported by LSMs when a process has the capability granted by DAC, but denied by an LSM. In the case of SELinux such denials are a problem, since they can't be effectively filtered out via the policy and when not silenced, they produce noise that may hide a true problem or an attack.
Checking for the capability only if any trusted xattr is actually present wouldn't really address the issue, since calling listxattr(2) on such node on its own doesn't indicate an explicit attempt to see the trusted xattrs. Additionally, it could potentially leak the presence of trusted xattrs to an unprivileged user if they can check for the denials (e.g. through dmesg).
Therefore, it's best (and simplest) to keep the check unconditional and instead use ns_capable_noaudit() that will silence any associated LSM denials.
Fixes: 38f38657444d ("xattr: extract simple_xattr code from tmpfs") Reported-by: Martin Pitt mpitt@redhat.com Suggested-by: Christian Brauner (Microsoft) brauner@kernel.org Signed-off-by: Ondrej Mosnacek omosnace@redhat.com Reviewed-by: Christian Brauner (Microsoft) brauner@kernel.org Reviewed-by: Paul Moore paul@paul-moore.com Signed-off-by: Christian Brauner (Microsoft) brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/xattr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/xattr.c b/fs/xattr.c index c0fd99c95aa1..d66983d1e57c 100644 --- a/fs/xattr.c +++ b/fs/xattr.c @@ -1017,7 +1017,7 @@ static int xattr_list_one(char **buffer, ssize_t *remaining_size, ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs, char *buffer, size_t size) { - bool trusted = capable(CAP_SYS_ADMIN); + bool trusted = ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN); struct simple_xattr *xattr; ssize_t remaining_size = size; int err = 0;