btrfs-util: be more careful when invoking btrfs file system ioctls

If we get passed an fd that does not refer to a regular file or
directory, we should not issue btrfs ioctls on it, since it might end up
in a device driver or similar (note that DRM for example uses the same
ioctl numbers as some file system ioctls).

Hence, let's make sure to always check if something is a regular file or
directory, or is on btrfs before invoking the respective ioctls. It's
better to be safe than sorry.

src/shared/btrfs-util.c

@@ -38,6 +38,14 @@
 #include "btrfs-ctree.h"
 #include "btrfs-util.h"
 
+/* WARNING: Be careful with file system ioctls! When we get an fd, we
+ * need to make sure it either refers to only a regular file or
+ * directory, or that it is located on btrfs, before invoking any
+ * btrfs ioctls. The ioctl numbers are reused by some device drivers
+ * (such as DRM), and hence might have bad effects when invoked on
+ * device nodes (that reference drivers) rather than fds to normal
+ * files or directories. */
+
 static int validate_subvolume_name(const char *name) {
 
         if (!filename_is_valid(name))
@@ -193,6 +201,15 @@ int btrfs_subvol_set_read_only(const char *path, bool b) {
 
 int btrfs_subvol_get_read_only_fd(int fd) {
         uint64_t flags;
+        struct stat st;
+
+        assert(fd >= 0);
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (!S_ISDIR(st.st_mode) || st.st_ino != 256)
+                return -EINVAL;
 
         if (ioctl(fd, BTRFS_IOC_SUBVOL_GETFLAGS, &flags) < 0)
                 return -errno;
@@ -201,11 +218,21 @@ int btrfs_subvol_get_read_only_fd(int fd) {
 }
 
 int btrfs_reflink(int infd, int outfd) {
+        struct stat st;
         int r;
 
         assert(infd >= 0);
         assert(outfd >= 0);
 
+        /* Make sure we invoke the ioctl on a regular file, so that no
+         * device driver accidentally gets it. */
+
+        if (fstat(outfd, &st) < 0)
+                return -errno;
+
+        if (!S_ISREG(st.st_mode))
+                return -EINVAL;
+
         r = ioctl(outfd, BTRFS_IOC_CLONE, infd);
         if (r < 0)
                 return -errno;
@@ -220,12 +247,19 @@ int btrfs_clone_range(int infd, uint64_t in_offset, int outfd, uint64_t out_offs
                 .src_length = sz,
                 .dest_offset = out_offset,
         };
+        struct stat st;
         int r;
 
         assert(infd >= 0);
         assert(outfd >= 0);
         assert(sz > 0);
 
+        if (fstat(outfd, &st) < 0)
+                return -errno;
+
+        if (!S_ISREG(st.st_mode))
+                return -EINVAL;
+
         r = ioctl(outfd, BTRFS_IOC_CLONE_RANGE, &args);
         if (r < 0)
                 return -errno;
@@ -236,10 +270,17 @@ int btrfs_clone_range(int infd, uint64_t in_offset, int outfd, uint64_t out_offs
 int btrfs_get_block_device_fd(int fd, dev_t *dev) {
         struct btrfs_ioctl_fs_info_args fsi = {};
         uint64_t id;
+        int r;
 
         assert(fd >= 0);
         assert(dev);
 
+        r = btrfs_is_filesystem(fd);
+        if (r < 0)
+                return r;
+        if (!r)
+                return -ENOTTY;
+
         if (ioctl(fd, BTRFS_IOC_FS_INFO, &fsi) < 0)
                 return -errno;
 
@@ -293,10 +334,17 @@ int btrfs_subvol_get_id_fd(int fd, uint64_t *ret) {
         struct btrfs_ioctl_ino_lookup_args args = {
                 .objectid = BTRFS_FIRST_FREE_OBJECTID
         };
+        int r;
 
         assert(fd >= 0);
         assert(ret);
 
+        r = btrfs_is_filesystem(fd);
+        if (r < 0)
+                return r;
+        if (!r)
+                return -ENOTTY;
+
         if (ioctl(fd, BTRFS_IOC_INO_LOOKUP, &args) < 0)
                 return -errno;
 
@@ -562,8 +610,16 @@ finish:
 }
 
 int btrfs_defrag_fd(int fd) {
+        struct stat st;
+
         assert(fd >= 0);
 
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (!S_ISREG(st.st_mode))
+                return -EINVAL;
+
         if (ioctl(fd, BTRFS_IOC_DEFRAG, NULL) < 0)
                 return -errno;
 
@@ -584,9 +640,16 @@ int btrfs_quota_enable_fd(int fd, bool b) {
         struct btrfs_ioctl_quota_ctl_args args = {
                 .cmd = b ? BTRFS_QUOTA_CTL_ENABLE : BTRFS_QUOTA_CTL_DISABLE,
         };
+        int r;
 
         assert(fd >= 0);
 
+        r = btrfs_is_filesystem(fd);
+        if (r < 0)
+                return r;
+        if (!r)
+                return -ENOTTY;
+
         if (ioctl(fd, BTRFS_IOC_QUOTA_CTL, &args) < 0)
                 return -errno;
 
@@ -610,9 +673,16 @@ int btrfs_quota_limit_fd(int fd, uint64_t referenced_max) {
                         referenced_max == 0 ? 1 : referenced_max,
                 .lim.flags = BTRFS_QGROUP_LIMIT_MAX_RFER,
         };
+        int r;
 
         assert(fd >= 0);
 
+        r = btrfs_is_filesystem(fd);
+        if (r < 0)
+                return r;
+        if (!r)
+                return -ENOTTY;
+
         if (ioctl(fd, BTRFS_IOC_QGROUP_LIMIT, &args) < 0)
                 return -errno;
 
@@ -732,11 +802,18 @@ static int subvol_remove_children(int fd, const char *subvolume, uint64_t subvol
 
         struct btrfs_ioctl_vol_args vol_args = {};
         _cleanup_close_ int subvol_fd = -1;
+        struct stat st;
         int r;
 
         assert(fd >= 0);
         assert(subvolume);
 
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (!S_ISDIR(st.st_mode))
+                return -EINVAL;
+
         /* First, try to remove the subvolume. If it happens to be
          * already empty, this will just work. */
         strncpy(vol_args.name, subvolume, sizeof(vol_args.name)-1);