Commit eae8d825 authored Nov 06, 2017 by Qu Wenruo Committed by David Sterba Nov 27, 2017

btrfs: Fix wild memory access in compression level parser



[BUG]
Kernel panic when mounting with "-o compress" mount option.
KASAN will report like:
------
==================================================================
BUG: KASAN: wild-memory-access in strncmp+0x31/0xc0
Read of size 1 at addr d86735fce994f800 by task mount/662
...
Call Trace:
 dump_stack+0xe3/0x175
 kasan_report+0x163/0x370
 __asan_load1+0x47/0x50
 strncmp+0x31/0xc0
 btrfs_compress_str2level+0x20/0x70 [btrfs]
 btrfs_parse_options+0xff4/0x1870 [btrfs]
 open_ctree+0x2679/0x49f0 [btrfs]
 btrfs_mount+0x1b7f/0x1d30 [btrfs]
 mount_fs+0x49/0x190
 vfs_kern_mount.part.29+0xba/0x280
 vfs_kern_mount+0x13/0x20
 btrfs_mount+0x31e/0x1d30 [btrfs]
 mount_fs+0x49/0x190
 vfs_kern_mount.part.29+0xba/0x280
 do_mount+0xaad/0x1a00
 SyS_mount+0x98/0xe0
 entry_SYSCALL_64_fastpath+0x1f/0xbe
------

[Cause]
For 'compress' and 'compress_force' options, its token doesn't expect
any parameter so its args[0] contains uninitialized data.
Accessing args[0] will cause above wild memory access.

[Fix]
For Opt_compress and Opt_compress_force, set compression level to
the default.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ set the default in advance ]
Signed-off-by: David Sterba <dsterba@suse.com>

parent b77000ed

fs/btrfs/compression.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1529,5 +1529,5 @@ unsigned int btrfs_compress_str2level(const char *str)
		if (str[4] == ':' && '1' <= str[5] && str[5] <= '9' && str[6] == 0)
		return str[5] - '0';

		return 0;
		return BTRFS_ZLIB_DEFAULT_LEVEL;
		}

fs/btrfs/compression.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -34,6 +34,8 @@
		/* Maximum size of data before compression */
		#define BTRFS_MAX_UNCOMPRESSED (SZ_128K)

		#define BTRFS_ZLIB_DEFAULT_LEVEL 3

		struct compressed_bio {
		/* number of bios pending for this compressed extent */
		refcount_t pending_bios;

fs/btrfs/super.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -507,7 +507,16 @@ int btrfs_parse_options(struct btrfs_fs_info info, char options,
		token == Opt_compress_force \|\|
		strncmp(args[0].from, "zlib", 4) == 0) {
		compress_type = "zlib";

		info->compress_type = BTRFS_COMPRESS_ZLIB;
		info->compress_level = BTRFS_ZLIB_DEFAULT_LEVEL;
		/*
		* args[0] contains uninitialized data since
		* for these tokens we don't expect any
		* parameter.
		*/
		if (token != Opt_compress &&
		token != Opt_compress_force)
		info->compress_level =
		btrfs_compress_str2level(args[0].from);
		btrfs_set_opt(info->mount_opt, COMPRESS);

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