As Stefan pointed out, I misremembered what clang can do specifically,
and it turns out that the variable-length array at the end of the
structure did not work (a flexible array would have worked here
but not solved the problem):
fs/ext4/mballoc.c:2303:17: error: fields must have a constant size:
'variable length array in structure' extension will never be supported
ext4_grpblk_t counters[blocksize_bits + 2];
This reverts part of my previous patch, using a fixed-size array
again, but keeping the check for the array overflow.
Fixes: 2df2c3402fc8 ("ext4: fix warning about stack corruption")
Reported-by: Stefan Agner <stefan@xxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
fs/ext4/mballoc.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5a1052627a81..701085620cd8 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2300,7 +2300,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
EXT4_MAX_BLOCK_LOG_SIZE);
struct sg {
struct ext4_group_info info;
- ext4_grpblk_t counters[blocksize_bits + 2];
+ ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
} sg;
group--;
@@ -2309,6 +2309,9 @@ 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 = (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))) {
@@ -2320,7 +2323,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
buddy_loaded = 1;
}
- memcpy(&sg, ext4_get_group_info(sb, group), sizeof(sg));
+ memcpy(&sg, ext4_get_group_info(sb, group), i);
if (buddy_loaded)
ext4_mb_unload_buddy(&e4b);
--
2.9.0
