From: Kyle Lippincott <spectral@xxxxxxxxxx>
Memory sanitizer (msan) is detecting a use of an uninitialized variable
(`size`) in `read_attr_from_index`:
==2268==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x5651f3416504 in read_attr_from_index git/attr.c:868:11
#1 0x5651f3415530 in read_attr git/attr.c
#2 0x5651f3413d74 in bootstrap_attr_stack git/attr.c:968:6
#3 0x5651f3413d74 in prepare_attr_stack git/attr.c:1004:2
#4 0x5651f3413d74 in collect_some_attrs git/attr.c:1199:2
#5 0x5651f3413144 in git_check_attr git/attr.c:1345:2
#6 0x5651f34728da in convert_attrs git/convert.c:1320:2
#7 0x5651f3473425 in would_convert_to_git_filter_fd git/convert.c:1373:2
#8 0x5651f357a35e in index_fd git/object-file.c:2630:34
#9 0x5651f357aa15 in index_path git/object-file.c:2657:7
#10 0x5651f35db9d9 in add_to_index git/read-cache.c:766:7
#11 0x5651f35dc170 in add_file_to_index git/read-cache.c:799:9
#12 0x5651f321f9b2 in add_files git/builtin/add.c:346:7
#13 0x5651f321f9b2 in cmd_add git/builtin/add.c:565:18
#14 0x5651f321d327 in run_builtin git/git.c:474:11
#15 0x5651f321bc9e in handle_builtin git/git.c:729:3
#16 0x5651f321a792 in run_argv git/git.c:793:4
#17 0x5651f321a792 in cmd_main git/git.c:928:19
#18 0x5651f33dde1f in main git/common-main.c:62:11
The issue exists because `size` is an output parameter from
`read_blob_data_from_index`, but it's only modified if
`read_blob_data_from_index` returns non-NULL. The read of `size` when
calling `read_attr_from_buf` unconditionally may read from an
uninitialized value. `read_attr_from_buf` checks that `buf` is non-NULL
before reading from `size`, but by then it's already too late: the
uninitialized read will have happened already. Furthermore, there's no
guarantee that the compiler won't reorder things so that it checks
`size` before checking `!buf`.
Make the call to `read_attr_from_buf` conditional on `buf` being
non-NULL, ensuring that `size` is not read if it's never set.
Signed-off-by: Kyle Lippincott <spectral@xxxxxxxxxx>
---
attr: fix msan issue in read_attr_from_index
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1747%2Fspectral54%2Fmsan-attr-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1747/spectral54/msan-attr-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1747
attr.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/attr.c b/attr.c
index 300f994ba6e..a2e0775f7e5 100644
--- a/attr.c
+++ b/attr.c
@@ -865,7 +865,8 @@ static struct attr_stack *read_attr_from_index(struct index_state *istate,
stack = read_attr_from_blob(istate, &istate->cache[sparse_dir_pos]->oid, relative_path, flags);
} else {
buf = read_blob_data_from_index(istate, path, &size);
- stack = read_attr_from_buf(buf, size, path, flags);
+ if (buf)
+ stack = read_attr_from_buf(buf, size, path, flags);
}
return stack;
}
base-commit: 8d94cfb54504f2ec9edc7ca3eb5c29a3dd3675ae
--
gitgitgadget
