Commit 270ef410 authored Aug 11, 2020 by Eric Biggers Committed by Linus Torvalds Aug 12, 2020

fs/minix: reject too-large maximum file size



If the minix filesystem tries to map a very large logical block number to
its on-disk location, block_to_path() can return offsets that are too
large, causing out-of-bounds memory accesses when accessing indirect index
blocks.  This should be prevented by the check against the maximum file
size, but this doesn't work because the maximum file size is read directly
from the on-disk superblock and isn't validated itself.

Fix this by validating the maximum file size at mount time.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by:  <syzbot+c7d9ec7a1a7272dd71b3@syzkaller.appspotmail.com>
Reported-by:  <syzbot+3b7b03a0c28948054fb5@syzkaller.appspotmail.com>
Reported-by:  <syzbot+6e056ee473568865f3e6@syzkaller.appspotmail.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Qiujun Huang <anenbupt@gmail.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200628060846.682158-4-ebiggers@kernel.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent facb03dd

fs/minix/inode.c

+20 −2

Original line number	Diff line number	Diff line
		@@ -150,6 +150,23 @@ static int minix_remount (struct super_block * sb, int * flags, char * data)
		return 0;
		}

		static bool minix_check_superblock(struct minix_sb_info *sbi)
		{
		if (sbi->s_imap_blocks == 0 \|\| sbi->s_zmap_blocks == 0)
		return false;

		/*
		* s_max_size must not exceed the block mapping limitation. This check
		* is only needed for V1 filesystems, since V2/V3 support an extra level
		* of indirect blocks which places the limit well above U32_MAX.
		*/
		if (sbi->s_version == MINIX_V1 &&
		sbi->s_max_size > (7 + 512 + 512512) BLOCK_SIZE)
		return false;

		return true;
		}

		static int minix_fill_super(struct super_block s, void data, int silent)
		{
		struct buffer_head *bh;
		@@ -228,11 +245,12 @@ static int minix_fill_super(struct super_block s, void data, int silent)
		} else
		goto out_no_fs;

		if (!minix_check_superblock(sbi))
		goto out_illegal_sb;

		/*
		* Allocate the buffer map to keep the superblock small.
		*/
		if (sbi->s_imap_blocks == 0 \|\| sbi->s_zmap_blocks == 0)
		goto out_illegal_sb;
		i = (sbi->s_imap_blocks + sbi->s_zmap_blocks) * sizeof(bh);
		map = kzalloc(i, GFP_KERNEL);
		if (!map)

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