From 7bc9491645118c9461bd21099c31755ff6783593 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Fri, 15 Jul 2016 00:22:07 -0400 Subject: [PATCH] ext4: verify extent header depth Although the extent tree depth of 5 should enough be for the worst case of 2*32 extents of length 1, the extent tree code does not currently to merge nodes which are less than half-full with a sibling node, or to shrink the tree depth if possible. So it's possible, at least in theory, for the tree depth to be greater than 5. However, even in the worst case, a tree depth of 32 is highly unlikely, and if the file system is maliciously corrupted, an insanely large eh_depth can cause memory allocation failures that will trigger kernel warnings (here, eh_depth = 65280): JBD2: ext4.exe wants too many credits credits:195849 rsv_credits:0 max:256 ------------[ cut here ]------------ WARNING: CPU: 0 PID: 50 at fs/jbd2/transaction.c:293 start_this_handle+0x569/0x580 CPU: 0 PID: 50 Comm: ext4.exe Not tainted 4.7.0-rc5+ #508 Stack: 604a8947 625badd8 0002fd09 00000000 60078643 00000000 62623910 601bf9bc 62623970 6002fc84 626239b0 900000125 Call Trace: [<6001c2dc>] show_stack+0xdc/0x1a0 [<601bf9bc>] dump_stack+0x2a/0x2e [<6002fc84>] __warn+0x114/0x140 [<6002fdff>] warn_slowpath_null+0x1f/0x30 [<60165829>] start_this_handle+0x569/0x580 [<60165d4e>] jbd2__journal_start+0x11e/0x220 [<60146690>] __ext4_journal_start_sb+0x60/0xa0 [<60120a81>] ext4_truncate+0x131/0x3a0 [<60123677>] ext4_setattr+0x757/0x840 [<600d5d0f>] notify_change+0x16f/0x2a0 [<600b2b16>] do_truncate+0x76/0xc0 [<600c3e56>] path_openat+0x806/0x1300 [<600c55c9>] do_filp_open+0x89/0xf0 [<600b4074>] do_sys_open+0x134/0x1e0 [<600b4140>] SyS_open+0x20/0x30 [<6001ea68>] handle_syscall+0x88/0x90 [<600295fd>] userspace+0x3fd/0x500 [<6001ac55>] fork_handler+0x85/0x90 ---[ end trace 08b0b88b6387a244 ]--- [ Commit message modified and the extent tree depath check changed from 5 to 32 -- tytso ] Cc: Darrick J. Wong Signed-off-by: Vegard Nossum Signed-off-by: Theodore Ts'o --- fs/ext4/extents.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 2f258c68d3e0..d7ccb7f51dfc 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -478,6 +478,10 @@ static int __ext4_ext_check(const char *function, unsigned int line, error_msg = "invalid extent entries"; goto corrupted; } + if (unlikely(depth > 32)) { + error_msg = "too large eh_depth"; + goto corrupted; + } /* Verify checksum on non-root extent tree nodes */ if (ext_depth(inode) != depth && !ext4_extent_block_csum_verify(inode, eh)) {