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libselinux: do not dereference symlink with statfs in selinux_restorecon

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When selinux_restorecon() is used to relabel symlinks, it performs the
following syscalls (as seen by running strace on restorecond):

    lstat("/root/symlink", {st_mode=S_IFLNK|0777, st_size=6, ...}) = 0
    statfs("/root/symlink", 0x7ffd6bb4d090) = -1 ENOENT (No such file or directory)
    lstat("/root/symlink", {st_mode=S_IFLNK|0777, st_size=6, ...}) = 0
    lgetxattr("/root/symlink", "security.selinux", "sysadm_u:object_r:user_home_t", 255) = 30

The second one triggers a SELinux check for lnk_file:read, as statfs()
dereferences symbolic links. This call to statfs() is only used to find
out whether "restoreconlast" xattr can be ignored, which is always the
case for non-directory files (the first syscall, lstat(), is actually
used to perform this check).

Skip the call to statfs() when setrestoreconlast is already false.

This silences an AVC denial that would otherwise be reported to
audit.log (cf. https://github.com/SELinuxProject/refpolicy/pull/22).

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
This commit is contained in:
Nicolas Iooss 2019-01-16 21:57:10 +01:00 committed by stephensmalley
parent c78f9c355f
commit 689a6eb576
1 changed files with 1 additions and 1 deletions
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2
libselinux/src/selinux_restorecon.c
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@ -881,7 +881,7 @@ int selinux_restorecon(const char *pathname_orig,
setrestoreconlast = false;
/* Ignore restoreconlast on in-memory filesystems */
if (statfs(pathname, &sfsb) == 0) {
if (setrestoreconlast && statfs(pathname, &sfsb) == 0) {
if (sfsb.f_type == RAMFS_MAGIC || sfsb.f_type == TMPFS_MAGIC)
setrestoreconlast = false;
}