ext4: fix warning about stack corruption (2df2c340) · Commits · 戴 / test

After commit 62d1034f53e3 ("fortify: use WARN instead of BUG for now"), we get a warning about possible stack overflow from a memcpy that was not strictly bounded to the size of the local variable: inlined from 'ext4_mb_seq_groups_show' at fs/ext4/mballoc.c:2322:2: include/linux/string.h:309:9: error: '__builtin_memcpy': writing between 161 and 1116 bytes into a region of size 160 overflows the destination [-Werror=stringop-overflow=] We actually had a bug here that would have been found by the warning, but it was already fixed last year in commit ("ext4: fix stack memory corruption with 64k block size"). This replaces the fixed-length structure on the stack with a variable-length structure, using the correct upper bound that tells the compiler that everything is really fine here. I also change the loop count to check for the same upper bound for consistency, but the existing code is already correct here. Note that while clang won't allow certain kinds of variable-length arrays in structures, this particular instance is fine, as the array is at the end of the structure, and the size is strictly bounded. Signed-off-by:

Arnd Bergmann <arnd@arndb.de> Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -2295,9 +2295,12 @@ static int ext4_mb_seq_groups_show(struct seq_file seq, void v)
		int err, buddy_loaded = 0;
		struct ext4_buddy e4b;
		struct ext4_group_info *grinfo;
		unsigned char blocksize_bits = min_t(unsigned char,
		sb->s_blocksize_bits,
		EXT4_MAX_BLOCK_LOG_SIZE);
		struct sg {
		struct ext4_group_info info;
		ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
		ext4_grpblk_t counters[blocksize_bits + 2];
		} sg;

		group--;
		@@ -2306,8 +2309,6 @@ static int ext4_mb_seq_groups_show(struct seq_file seq, void v)
		" 2^0 2^1 2^2 2^3 2^4 2^5 2^6 "
		" 2^7 2^8 2^9 2^10 2^11 2^12 2^13 ]\n");

		i = (sb->s_blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
		sizeof(struct ext4_group_info);
		grinfo = ext4_get_group_info(sb, group);
		/* Load the group info in memory only if not already loaded. */
		if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
		@@ -2319,7 +2320,7 @@ static int ext4_mb_seq_groups_show(struct seq_file seq, void v)
		buddy_loaded = 1;
		}

		memcpy(&sg, ext4_get_group_info(sb, group), i);
		memcpy(&sg, ext4_get_group_info(sb, group), sizeof(sg));

		if (buddy_loaded)
		ext4_mb_unload_buddy(&e4b);
		@@ -2327,7 +2328,7 @@ static int ext4_mb_seq_groups_show(struct seq_file seq, void v)
		seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
		sg.info.bb_fragments, sg.info.bb_first_free);
		for (i = 0; i <= 13; i++)
		seq_printf(seq, " %-5u", i <= sb->s_blocksize_bits + 1 ?
		seq_printf(seq, " %-5u", i <= blocksize_bits + 1 ?
		sg.info.bb_counters[i] : 0);
		seq_printf(seq, " ]\n");

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