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Just a single fix for an annoying regression introduced in 2.9 when fixing 

CVE-2016-9602.
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Merge remote-tracking branch 'remotes/gkurz/tags/for-upstream' into staging

Just a single fix for an annoying regression introduced in 2.9 when fixing
CVE-2016-9602.

# gpg: Signature made Thu 10 Aug 2017 13:40:28 BST
# gpg:                using DSA key 0x02FC3AEB0101DBC2
# gpg: Good signature from "Greg Kurz <groug@kaod.org>"
# gpg:                 aka "Greg Kurz <groug@free.fr>"
# gpg:                 aka "Greg Kurz <gkurz@linux.vnet.ibm.com>"
# gpg:                 aka "Gregory Kurz (Groug) <groug@free.fr>"
# gpg:                 aka "[jpeg image of size 3330]"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 2BD4 3B44 535E C0A7 9894  DBA2 02FC 3AEB 0101 DBC2

* remotes/gkurz/tags/for-upstream:
  9pfs: local: fix fchmodat_nofollow() limitations

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Peter Maydell 2017-08-10 17:50:55 +01:00
parent b38df311c1 4751fd5328
commit 473a321122
2 changed files with 50 additions and 16 deletions
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42
hw/9pfs/9p-local.c
View File

@ -333,17 +333,27 @@ update_map_file:
static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode)
{
struct stat stbuf;
int fd, ret;
/* FIXME: this should be handled with fchmodat(AT_SYMLINK_NOFOLLOW).
* Unfortunately, the linux kernel doesn't implement it yet. As an
* alternative, let's open the file and use fchmod() instead. This
* may fail depending on the permissions of the file, but it is the
* best we can do to avoid TOCTTOU. We first try to open read-only
* in case name points to a directory. If that fails, we try write-only
* in case name doesn't point to a directory.
* Unfortunately, the linux kernel doesn't implement it yet.
*/
fd = openat_file(dirfd, name, O_RDONLY, 0);
/* First, we clear non-racing symlinks out of the way. */
if (fstatat(dirfd, name, &stbuf, AT_SYMLINK_NOFOLLOW)) {
return -1;
}
if (S_ISLNK(stbuf.st_mode)) {
errno = ELOOP;
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);
#if O_PATH_9P_UTIL == 0
if (fd == -1) {
/* In case the file is writable-only and isn't a directory. */
if (errno == EACCES) {
@ -357,6 +367,24 @@ static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode)
return -1;
}
ret = fchmod(fd, mode);
#else
if (fd == -1) {
return -1;
}
/* Now we handle racing symlinks. */
ret = fstat(fd, &stbuf);
if (!ret) {
if (S_ISLNK(stbuf.st_mode)) {
errno = ELOOP;
ret = -1;
} else {
char *proc_path = g_strdup_printf("/proc/self/fd/%d", fd);
ret = chmod(proc_path, mode);
g_free(proc_path);
}
}
#endif
close_preserve_errno(fd);
return ret;
}

24
hw/9pfs/9p-util.h
View File

@ -13,6 +13,12 @@
#ifndef QEMU_9P_UTIL_H
#define QEMU_9P_UTIL_H
#ifdef O_PATH
#define O_PATH_9P_UTIL O_PATH
#else
#define O_PATH_9P_UTIL 0
#endif
static inline void close_preserve_errno(int fd)
{
int serrno = errno;
@ -22,13 +28,8 @@ static inline void close_preserve_errno(int fd)
static inline int openat_dir(int dirfd, const char *name)
{
#ifdef O_PATH
#define OPENAT_DIR_O_PATH O_PATH
#else
#define OPENAT_DIR_O_PATH 0
#endif
return openat(dirfd, name,
O_DIRECTORY | O_RDONLY | O_NOFOLLOW | OPENAT_DIR_O_PATH);
O_DIRECTORY | O_RDONLY | O_NOFOLLOW | O_PATH_9P_UTIL);
}
static inline int openat_file(int dirfd, const char *name, int flags,
@ -43,9 +44,14 @@ static inline int openat_file(int dirfd, const char *name, int flags,
}
serrno = errno;
/* O_NONBLOCK was only needed to open the file. Let's drop it. */
ret = fcntl(fd, F_SETFL, flags);
assert(!ret);
/* O_NONBLOCK was only needed to open the file. Let's drop it. We don't
* do that with O_PATH since fcntl(F_SETFL) isn't supported, and openat()
* ignored it anyway.
*/
if (!(flags & O_PATH_9P_UTIL)) {
ret = fcntl(fd, F_SETFL, flags);
assert(!ret);
}
errno = serrno;
return fd;
}