The squashfs driver blindly follows symlinks, and calls sqfs_size() recursively. So an attacker can create a crafted filesystem and with a deep enough nesting level a stack overflow can be achieved.
Fix by limiting the nesting level to 8.
Signed-off-by: Richard Weinberger richard@nod.at --- fs/squashfs/sqfs.c | 74 ++++++++++++++++++++++++++++++++++++---------- 1 file changed, 59 insertions(+), 15 deletions(-)
diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c index fa99d514f2..3b23c5bc8f 100644 --- a/fs/squashfs/sqfs.c +++ b/fs/squashfs/sqfs.c @@ -25,6 +25,9 @@ #include "sqfs_utils.h"
static struct squashfs_ctxt ctxt; +static int symlinknest; + +static int sqfs_readdir_nest(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp);
static int sqfs_disk_read(__u32 block, __u32 nr_blocks, void *buf) { @@ -510,7 +513,7 @@ static int sqfs_search_dir(struct squashfs_dir_stream *dirs, char **token_list, goto out; }
- while (!sqfs_readdir(dirsp, &dent)) { + while (!sqfs_readdir_nest(dirsp, &dent)) { ret = strcmp(dent->name, token_list[j]); if (!ret) break; @@ -537,6 +540,11 @@ static int sqfs_search_dir(struct squashfs_dir_stream *dirs, char **token_list,
/* Check for symbolic link and inode type sanity */ if (get_unaligned_le16(&dir->inode_type) == SQFS_SYMLINK_TYPE) { + if (++symlinknest == 8) { + ret = -ELOOP; + goto out; + } + sym = (struct squashfs_symlink_inode *)table; /* Get first j + 1 tokens */ path = sqfs_concat_tokens(token_list, j + 1); @@ -884,7 +892,7 @@ out: return metablks_count; }
-int sqfs_opendir(const char *filename, struct fs_dir_stream **dirsp) +static int sqfs_opendir_nest(const char *filename, struct fs_dir_stream **dirsp) { unsigned char *inode_table = NULL, *dir_table = NULL; int j, token_count = 0, ret = 0, metablks_count; @@ -979,7 +987,19 @@ out: return ret; }
+int sqfs_opendir(const char *filename, struct fs_dir_stream **dirsp) +{ + symlinknest = 0; + return sqfs_opendir_nest(filename, dirsp); +} + int sqfs_readdir(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp) +{ + symlinknest = 0; + return sqfs_readdir_nest(fs_dirs, dentp); +} + +static int sqfs_readdir_nest(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp) { struct squashfs_super_block *sblk = ctxt.sblk; struct squashfs_dir_stream *dirs; @@ -1325,8 +1345,8 @@ static int sqfs_get_lregfile_info(struct squashfs_lreg_inode *lreg, return datablk_count; }
-int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len, - loff_t *actread) +static int sqfs_read_nest(const char *filename, void *buf, loff_t offset, + loff_t len, loff_t *actread) { char *dir = NULL, *fragment_block, *datablock = NULL; char *fragment = NULL, *file = NULL, *resolved, *data; @@ -1356,11 +1376,11 @@ int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len, }
/* - * sqfs_opendir will uncompress inode and directory tables, and will + * sqfs_opendir_nest will uncompress inode and directory tables, and will * return a pointer to the directory that contains the requested file. */ sqfs_split_path(&file, &dir, filename); - ret = sqfs_opendir(dir, &dirsp); + ret = sqfs_opendir_nest(dir, &dirsp); if (ret) { goto out; } @@ -1368,7 +1388,7 @@ int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len, dirs = (struct squashfs_dir_stream *)dirsp;
/* For now, only regular files are able to be loaded */ - while (!sqfs_readdir(dirsp, &dent)) { + while (!sqfs_readdir_nest(dirsp, &dent)) { ret = strcmp(dent->name, file); if (!ret) break; @@ -1421,9 +1441,14 @@ int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len, break; case SQFS_SYMLINK_TYPE: case SQFS_LSYMLINK_TYPE: + if (++symlinknest == 8) { + ret = -ELOOP; + goto out; + } + symlink = (struct squashfs_symlink_inode *)ipos; resolved = sqfs_resolve_symlink(symlink, filename); - ret = sqfs_read(resolved, buf, offset, len, actread); + ret = sqfs_read_nest(resolved, buf, offset, len, actread); free(resolved); goto out; case SQFS_BLKDEV_TYPE: @@ -1594,7 +1619,14 @@ out: return ret; }
-int sqfs_size(const char *filename, loff_t *size) +int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len, + loff_t *actread) +{ + symlinknest = 0; + return sqfs_read_nest(filename, buf, offset, len, actread); +} + +static int sqfs_size_nest(const char *filename, loff_t *size) { struct squashfs_super_block *sblk = ctxt.sblk; struct squashfs_symlink_inode *symlink; @@ -1610,10 +1642,10 @@ int sqfs_size(const char *filename, loff_t *size)
sqfs_split_path(&file, &dir, filename); /* - * sqfs_opendir will uncompress inode and directory tables, and will + * sqfs_opendir_nest will uncompress inode and directory tables, and will * return a pointer to the directory that contains the requested file. */ - ret = sqfs_opendir(dir, &dirsp); + ret = sqfs_opendir_nest(dir, &dirsp); if (ret) { ret = -EINVAL; goto free_strings; @@ -1621,7 +1653,7 @@ int sqfs_size(const char *filename, loff_t *size)
dirs = (struct squashfs_dir_stream *)dirsp;
- while (!sqfs_readdir(dirsp, &dent)) { + while (!sqfs_readdir_nest(dirsp, &dent)) { ret = strcmp(dent->name, file); if (!ret) break; @@ -1661,6 +1693,11 @@ int sqfs_size(const char *filename, loff_t *size) break; case SQFS_SYMLINK_TYPE: case SQFS_LSYMLINK_TYPE: + if (++symlinknest == 8) { + *size = 0; + return -ELOOP; + } + symlink = (struct squashfs_symlink_inode *)ipos; resolved = sqfs_resolve_symlink(symlink, filename); ret = sqfs_size(resolved, size); @@ -1700,10 +1737,11 @@ int sqfs_exists(const char *filename)
sqfs_split_path(&file, &dir, filename); /* - * sqfs_opendir will uncompress inode and directory tables, and will + * sqfs_opendir_nest will uncompress inode and directory tables, and will * return a pointer to the directory that contains the requested file. */ - ret = sqfs_opendir(dir, &dirsp); + symlinknest = 0; + ret = sqfs_opendir_nest(dir, &dirsp); if (ret) { ret = -EINVAL; goto free_strings; @@ -1711,7 +1749,7 @@ int sqfs_exists(const char *filename)
dirs = (struct squashfs_dir_stream *)dirsp;
- while (!sqfs_readdir(dirsp, &dent)) { + while (!sqfs_readdir_nest(dirsp, &dent)) { ret = strcmp(dent->name, file); if (!ret) break; @@ -1728,6 +1766,12 @@ free_strings: return ret == 0; }
+int sqfs_size(const char *filename, loff_t *size) +{ + symlinknest = 0; + return sqfs_size_nest(filename, size); +} + void sqfs_close(void) { sqfs_decompressor_cleanup(&ctxt);