Commit aa5e85a1 authored by Greg Kurz's avatar Greg Kurz
Browse files

9pfs: local: clarify fchmodat_nofollow() implementation 



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: default avatarGreg Kurz <groug@kaod.org>
Reviewed-by: default avatarPhilippe Mathieu-Daudé <f4bug@amsat.org>
parent 3c08f4a4

hw/9pfs/9p-local.c

+8 −4
Original line number Diff line number Diff line
@@ -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;

    }