https://bugzilla.kernel.org/show_bug.cgi?id=194567 Eric Sandeen (sandeen@xxxxxxxxxxx) changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |sandeen@xxxxxxxxxxx --- Comment #1 from Eric Sandeen (sandeen@xxxxxxxxxxx) --- Can you add the dumpe2fs -h output for the device? I guess this would be thanks to: http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.4.y&id=e21a3cad35bc2f4c7fff317e2c7d38eed363a430 ext4: validate s_first_meta_bg at mount time commit 3a4b77cd47bb837b8557595ec7425f281f2ca1fe upstream. Ralf Spenneberg reported that he hit a kernel crash when mounting a modified ext4 image. And it turns out that kernel crashed when calculating fs overhead (ext4_calculate_overhead()), this is because the image has very large s_first_meta_bg (debug code shows it's 842150400), and ext4 overruns the memory in count_overhead() when setting bitmap buffer, which is PAGE_SIZE. ext4_calculate_overhead(): buf = get_zeroed_page(GFP_NOFS); <=== PAGE_SIZE buffer blks = count_overhead(sb, i, buf); count_overhead(): for (j = ext4_bg_num_gdb(sb, grp); j > 0; j--) { <=== j = 842150400 ext4_set_bit(EXT4_B2C(sbi, s++), buf); <=== buffer overrun count++; } This can be reproduced easily for me by this script: #!/bin/bash rm -f fs.img mkdir -p /mnt/ext4 fallocate -l 16M fs.img mke2fs -t ext4 -O bigalloc,meta_bg,^resize_inode -F fs.img debugfs -w -R "ssv first_meta_bg 842150400" fs.img mount -o loop fs.img /mnt/ext4 Fix it by validating s_first_meta_bg first at mount time, and refusing to mount if its value exceeds the largest possible meta_bg number. Reported-by: Ralf Spenneberg <ralf@xxxxxxx> Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> -- You are receiving this mail because: You are watching the assignee of the bug.
