From: Wang Shilong Date: Mon, 30 Dec 2019 19:52:39 -0500 Subject: e2fsck: fix use after free in calculate_tree() The problem is alloc_blocks() will call get_next_block() which might reallocate outdir->buf, and memory address could be changed after this. To fix this, pointers that point into outdir->buf, such as int_limit and root need to be recaulated based on the new starting address of outdir->buf. [ Changed to correctly recalculate int_limit, and to optimize how we reallocate outdir->buf. -TYT ] Addresses-Debian-Bug: 948517 Signed-off-by: Wang Shilong Signed-off-by: Theodore Ts'o (cherry picked from commit 101e73e99ccafa0403fcb27dd7413033b587ca01) Signed-off-by: Anuj Mittal Upstream-Status: Backport [https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/commit/?id=101e73e99ccafa0403fcb27dd7413033b587ca01] --- e2fsck/rehash.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/e2fsck/rehash.c b/e2fsck/rehash.c index 0a5888a9..2574e151 100644 --- a/e2fsck/rehash.c +++ b/e2fsck/rehash.c @@ -295,7 +295,11 @@ static errcode_t get_next_block(ext2_filsys fs, struct out_dir *outdir, errcode_t retval; if (outdir->num >= outdir->max) { - retval = alloc_size_dir(fs, outdir, outdir->max + 50); + int increment = outdir->max / 10; + + if (increment < 50) + increment = 50; + retval = alloc_size_dir(fs, outdir, outdir->max + increment); if (retval) return retval; } @@ -637,6 +641,9 @@ static int alloc_blocks(ext2_filsys fs, if (retval) return retval; + /* outdir->buf might be reallocated */ + *prev_ent = (struct ext2_dx_entry *) (outdir->buf + *prev_offset); + *next_ent = set_int_node(fs, block_start); *limit = (struct ext2_dx_countlimit *)(*next_ent); if (next_offset) @@ -726,6 +733,9 @@ static errcode_t calculate_tree(ext2_filsys fs, return retval; } if (c3 == 0) { + int delta1 = (char *)int_limit - outdir->buf; + int delta2 = (char *)root - outdir->buf; + retval = alloc_blocks(fs, &limit, &int_ent, &dx_ent, &int_offset, NULL, outdir, i, &c2, @@ -733,6 +743,11 @@ static errcode_t calculate_tree(ext2_filsys fs, if (retval) return retval; + /* outdir->buf might be reallocated */ + int_limit = (struct ext2_dx_countlimit *) + (outdir->buf + delta1); + root = (struct ext2_dx_entry *) + (outdir->buf + delta2); } dx_ent->block = ext2fs_cpu_to_le32(i); if (c3 != limit->limit) -- 2.24.1