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: Greg Kurz <groug@kaod.org> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
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@ -349,11 +349,11 @@ static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode)
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return -1;
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return -1;
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}
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}
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/* Access modes are ignored when O_PATH is supported. We try O_RDONLY and
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fd = openat_file(dirfd, name, O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
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* O_WRONLY for old-systems that don't support O_PATH.
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*/
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fd = openat_file(dirfd, name, O_RDONLY | O_PATH_9P_UTIL, 0);
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#if O_PATH_9P_UTIL == 0
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#if O_PATH_9P_UTIL == 0
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/* Fallback for systems that don't support O_PATH: we depend on the file
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* being readable or writable.
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*/
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if (fd == -1) {
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if (fd == -1) {
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/* In case the file is writable-only and isn't a directory. */
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/* In case the file is writable-only and isn't a directory. */
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if (errno == EACCES) {
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if (errno == EACCES) {
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@ -368,6 +368,10 @@ static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode)
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}
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}
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ret = fchmod(fd, mode);
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ret = fchmod(fd, mode);
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#else
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#else
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/* Access modes are ignored when O_PATH is supported. If name is a symbolic
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* link, O_PATH | O_NOFOLLOW causes openat(2) to return a file descriptor
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* referring to the symbolic link.
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*/
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if (fd == -1) {
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if (fd == -1) {
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return -1;
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return -1;
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}
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}
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