On 09/04/2017 04:24 AM, Greg Kurz wrote:
Since fchmodat(2) on Linux doesn't support AT_SYMLINK_NOFOLLOW, we have to
implement it using workarounds. There are two different ways, depending on
whether the system supports O_PATH or not.
In the case O_PATH is supported, we rely on the behavhior of openat(2)
when passing O_NOFOLLOW | O_PATH and the file is a symbolic link. Even
if openat_file() already adds O_NOFOLLOW to the flags, this patch makes
it explicit that we need both creation flags to obtain the expected
behavior.
This is only cleanup, no functional change.
Signed-off-by: Greg Kurz <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
---
hw/9pfs/9p-local.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index efb0b79a74bf..e51af87309c6 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -349,11 +349,11 @@ static int fchmodat_nofollow(int dirfd, const char *name,
mode_t mode)
return -1;
}
- /* Access modes are ignored when O_PATH is supported. We try O_RDONLY and
- * O_WRONLY for old-systems that don't support O_PATH.
- */
- fd = openat_file(dirfd, name, O_RDONLY | O_PATH_9P_UTIL, 0);
+ fd = openat_file(dirfd, name, O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
#if O_PATH_9P_UTIL == 0
+ /* Fallback for systems that don't support O_PATH: we depend on the file
+ * being readable or writable.
+ */
if (fd == -1) {
/* In case the file is writable-only and isn't a directory. */
if (errno == EACCES) {
@@ -368,6 +368,10 @@ static int fchmodat_nofollow(int dirfd, const char *name,
mode_t mode)
}
ret = fchmod(fd, mode);
#else
+ /* Access modes are ignored when O_PATH is supported. If name is a symbolic
+ * link, O_PATH | O_NOFOLLOW causes openat(2) to return a file descriptor
+ * referring to the symbolic link.
+ */
if (fd == -1) {
return -1;
}
