ext3: fix start and len arguments handling in ext3_trim_fs()

The overflow might happen when passing blocknr into
ext3_get_group_no_and_offset(), because it expects type ext3_fsblk_t
which might be smaller than uint64_t. This will most likely happen when
calling FITRIM with the default argument len = ULLONG_MAX.

Fix this by using "end" variable instead of "start+len" as it is easier
to get right and specifically check that the end is not beyond the end
of the file system, so we are sure that the result of
get_group_no_and_offset() will not overflow. Otherwise truncate it to
the size of the file system.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 39 insertions, 38 deletions

diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
index 954a7d355f59..1e036b79384c 100644
--- a/fs/ext3/balloc.c
+++ b/fs/ext3/balloc.c
@@ -1973,7 +1973,7 @@ static ext3_grpblk_t ext3_trim_all_free(struct super_block *sb,
         sbi = EXT3_SB(sb);
 
          /* Walk through the whole group */
-        while (start < max) {
+        while (start <= max) {
                 start = bitmap_search_next_usable_block(start, bitmap_bh, max);
                 if (start < 0)
                         break;
@@ -1983,7 +1983,7 @@ static ext3_grpblk_t ext3_trim_all_free(struct super_block *sb,
                  * Allocate contiguous free extents by setting bits in the
                  * block bitmap
                  */
-                while (next < max
+                while (next <= max
                         && claim_block(sb_bgl_lock(sbi, group),
                                         next, bitmap_bh)) {
                         next++;
@@ -2094,73 +2094,74 @@ err_out:
  */
 int ext3_trim_fs(struct super_block *sb, struct fstrim_range *range)
 {
-        ext3_grpblk_t last_block, first_block, free_blocks;
-        unsigned long first_group, last_group;
-        unsigned long group, ngroups;
+        ext3_grpblk_t last_block, first_block;
+        unsigned long group, first_group, last_group;
         struct ext3_group_desc *gdp;
         struct ext3_super_block *es = EXT3_SB(sb)->s_es;
-        uint64_t start, len, minlen, trimmed;
+        uint64_t start, minlen, end, trimmed = 0;
+        ext3_fsblk_t first_data_blk =
+                        le32_to_cpu(EXT3_SB(sb)->s_es->s_first_data_block);
         ext3_fsblk_t max_blks = le32_to_cpu(es->s_blocks_count);
         int ret = 0;
 
-        start = (range->start >> sb->s_blocksize_bits) +
-                le32_to_cpu(es->s_first_data_block);
-        len = range->len >> sb->s_blocksize_bits;
+        start = range->start >> sb->s_blocksize_bits;
+        end = start + (range->len >> sb->s_blocksize_bits) - 1;
         minlen = range->minlen >> sb->s_blocksize_bits;
-        trimmed = 0;
 
-        if (unlikely(minlen > EXT3_BLOCKS_PER_GROUP(sb)))
+        if (unlikely(minlen > EXT3_BLOCKS_PER_GROUP(sb)) ||
+            unlikely(start >= max_blks))
                 return -EINVAL;
-        if (start >= max_blks)
-                return -EINVAL;
-        if (start + len > max_blks)
-                len = max_blks - start;
+        if (end >= max_blks)
+                end = max_blks - 1;
+        if (end <= first_data_blk)
+                goto out;
+        if (start < first_data_blk)
+                start = first_data_blk;
 
-        ngroups = EXT3_SB(sb)->s_groups_count;
         smp_rmb();
 
         /* Determine first and last group to examine based on start and len */
         ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) start,
                                      &first_group, &first_block);
-        ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) (start + len),
+        ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) end,
                                      &last_group, &last_block);
-        last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
-        last_block = EXT3_BLOCKS_PER_GROUP(sb);
 
-        if (first_group > last_group)
-                return -EINVAL;
+        /* end now represents the last block to discard in this group */
+        end = EXT3_BLOCKS_PER_GROUP(sb) - 1;
 
         for (group = first_group; group <= last_group; group++) {
                 gdp = ext3_get_group_desc(sb, group, NULL);
                 if (!gdp)
                         break;
 
-                free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
-                if (free_blocks < minlen)
-                        continue;
-
                 /*
                  * For all the groups except the last one, last block will
-                 * always be EXT3_BLOCKS_PER_GROUP(sb), so we only need to
-                 * change it for the last group in which case first_block +
-                 * len < EXT3_BLOCKS_PER_GROUP(sb).
+                 * always be EXT3_BLOCKS_PER_GROUP(sb)-1, so we only need to
+                 * change it for the last group, note that last_block is
+                 * already computed earlier by ext3_get_group_no_and_offset()
                  */
-                if (first_block + len < EXT3_BLOCKS_PER_GROUP(sb))
-                        last_block = first_block + len;
-                len -= last_block - first_block;
+                if (group == last_group)
+                        end = last_block;
 
-                ret = ext3_trim_all_free(sb, group, first_block,
-                                        last_block, minlen);
-                if (ret < 0)
-                        break;
+                if (le16_to_cpu(gdp->bg_free_blocks_count) >= minlen) {
+                        ret = ext3_trim_all_free(sb, group, first_block,
+                                                 end, minlen);
+                        if (ret < 0)
+                                break;
+                        trimmed += ret;
+                }
 
-                trimmed += ret;
+                /*
+                 * For every group except the first one, we are sure
+                 * that the first block to discard will be block #0.
+                 */
                 first_block = 0;
         }
 
-        if (ret >= 0)
+        if (ret > 0)
                 ret = 0;
-        range->len = trimmed * sb->s_blocksize;
 
+out:
+        range->len = trimmed * sb->s_blocksize;
         return ret;
 }