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authorGreg Kurz <groug@kaod.org>2017-02-26 23:42:43 +0100
committerGreg Kurz <groug@kaod.org>2017-02-28 11:21:15 +0100
commit3e36aba757f76673007a80b3cd56a4062c2e3462 (patch)
treefde3ba123eb07da546df251adc8fc3c710949735
parent5507904e362df252f6065cb27d1ff98372db6abc (diff)
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9pfs: local: lsetxattr: don't follow symlinks
The local_lsetxattr() callback is vulnerable to symlink attacks because it calls lsetxattr() which follows symbolic links in all path elements but the rightmost one. This patch introduces a helper to emulate the non-existing fsetxattrat() function: it is implemented with /proc/self/fd which provides a trusted path that can be safely passed to lsetxattr(). local_lsetxattr() is converted to use this helper and opendir_nofollow(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
-rw-r--r--hw/9pfs/9p-posix-acl.c18
-rw-r--r--hw/9pfs/9p-util.h2
-rw-r--r--hw/9pfs/9p-xattr-user.c8
-rw-r--r--hw/9pfs/9p-xattr.c39
-rw-r--r--hw/9pfs/9p-xattr.h3
5 files changed, 43 insertions, 27 deletions
diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
index 9435e27..0154e2a 100644
--- a/hw/9pfs/9p-posix-acl.c
+++ b/hw/9pfs/9p-posix-acl.c
@@ -50,13 +50,8 @@ static ssize_t mp_pacl_listxattr(FsContext *ctx, const char *path,
static int mp_pacl_setxattr(FsContext *ctx, const char *path, const char *name,
void *value, size_t size, int flags)
{
- char *buffer;
- int ret;
-
- buffer = rpath(ctx, path);
- ret = lsetxattr(buffer, MAP_ACL_ACCESS, value, size, flags);
- g_free(buffer);
- return ret;
+ return local_setxattr_nofollow(ctx, path, MAP_ACL_ACCESS, value, size,
+ flags);
}
static int mp_pacl_removexattr(FsContext *ctx,
@@ -108,13 +103,8 @@ static ssize_t mp_dacl_listxattr(FsContext *ctx, const char *path,
static int mp_dacl_setxattr(FsContext *ctx, const char *path, const char *name,
void *value, size_t size, int flags)
{
- char *buffer;
- int ret;
-
- buffer = rpath(ctx, path);
- ret = lsetxattr(buffer, MAP_ACL_DEFAULT, value, size, flags);
- g_free(buffer);
- return ret;
+ return local_setxattr_nofollow(ctx, path, MAP_ACL_DEFAULT, value, size,
+ flags);
}
static int mp_dacl_removexattr(FsContext *ctx,
diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h
index 676641f..091f3ce 100644
--- a/hw/9pfs/9p-util.h
+++ b/hw/9pfs/9p-util.h
@@ -48,5 +48,7 @@ int relative_openat_nofollow(int dirfd, const char *path, int flags,
mode_t mode);
ssize_t fgetxattrat_nofollow(int dirfd, const char *path, const char *name,
void *value, size_t size);
+int fsetxattrat_nofollow(int dirfd, const char *path, const char *name,
+ void *value, size_t size, int flags);
#endif
diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c
index 4071fbc..1840a5d 100644
--- a/hw/9pfs/9p-xattr-user.c
+++ b/hw/9pfs/9p-xattr-user.c
@@ -67,9 +67,6 @@ static ssize_t mp_user_listxattr(FsContext *ctx, const char *path,
static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name,
void *value, size_t size, int flags)
{
- char *buffer;
- int ret;
-
if (strncmp(name, "user.virtfs.", 12) == 0) {
/*
* Don't allow fetch of user.virtfs namesapce
@@ -78,10 +75,7 @@ static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name,
errno = EACCES;
return -1;
}
- buffer = rpath(ctx, path);
- ret = lsetxattr(buffer, name, value, size, flags);
- g_free(buffer);
- return ret;
+ return local_setxattr_nofollow(ctx, path, name, value, size, flags);
}
static int mp_user_removexattr(FsContext *ctx,
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index 54193c6..a0167dd 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -195,18 +195,45 @@ ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name,
return local_getxattr_nofollow(ctx, path, name, value, size);
}
-int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value,
- size_t size, int flags)
+int fsetxattrat_nofollow(int dirfd, const char *filename, const char *name,
+ void *value, size_t size, int flags)
{
- char *buffer;
+ char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename);
int ret;
- buffer = rpath(ctx, path);
- ret = lsetxattr(buffer, name, value, size, flags);
- g_free(buffer);
+ ret = lsetxattr(proc_path, name, value, size, flags);
+ g_free(proc_path);
+ return ret;
+}
+
+ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,
+ const char *name, void *value, size_t size,
+ int flags)
+{
+ char *dirpath = g_path_get_dirname(path);
+ char *filename = g_path_get_basename(path);
+ int dirfd;
+ ssize_t ret = -1;
+
+ dirfd = local_opendir_nofollow(ctx, dirpath);
+ if (dirfd == -1) {
+ goto out;
+ }
+
+ ret = fsetxattrat_nofollow(dirfd, filename, name, value, size, flags);
+ close_preserve_errno(dirfd);
+out:
+ g_free(dirpath);
+ g_free(filename);
return ret;
}
+int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value,
+ size_t size, int flags)
+{
+ return local_setxattr_nofollow(ctx, path, name, value, size, flags);
+}
+
int pt_removexattr(FsContext *ctx, const char *path, const char *name)
{
char *buffer;
diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h
index 69a8b6b..7558970 100644
--- a/hw/9pfs/9p-xattr.h
+++ b/hw/9pfs/9p-xattr.h
@@ -31,6 +31,9 @@ typedef struct xattr_operations
ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path,
const char *name, void *value, size_t size);
+ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,
+ const char *name, void *value, size_t size,
+ int flags);
extern XattrOperations mapped_user_xattr;
extern XattrOperations passthrough_user_xattr;