Re: Null pointer dereference in git-submodule

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Am 24.03.2018 um 18:42 schrieb Jeremy Feusi:
> Hi,
> While bootstrapping a gnu repository I noticed that git segfaulted when
> called as "git submodule status". After compiling git with address
> sanitizer and minimizing the directory I finally narrowed it down to the
> files which I have attached as a tar archive. Here is a detailed backtrace:
> 
> AddressSanitizer:DEADLYSIGNAL
> =================================================================
> ==63400==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000c27a93 bp 0x7ffdcb4eec10 sp 0x7ffdcb4eeb80 T0)
> ==63400==The signal is caused by a READ memory access.
> ==63400==Hint: address points to the zero page.
>      #0 0xc27a92 in refs_read_raw_ref /home/jfe/git/refs.c:1451:20
>      #1 0xc174a6 in refs_resolve_ref_unsafe /home/jfe/git/refs.c:1493:7
>      #2 0xc1826a in refs_read_ref_full /home/jfe/git/refs.c:224:6
>      #3 0xc26d53 in refs_head_ref /home/jfe/git/refs.c:1314:7
>      #4 0x8071e6 in status_submodule /home/jfe/git/builtin/submodule--helper.c:658:7
>      #5 0x806a89 in status_submodule_cb /home/jfe/git/builtin/submodule--helper.c:699:2
>      #6 0x80523e in for_each_listed_submodule /home/jfe/git/builtin/submodule--helper.c:438:3
>      #7 0x7f7e9a in module_status /home/jfe/git/builtin/submodule--helper.c:732:2
>      #8 0x7efd69 in cmd_submodule__helper /home/jfe/git/builtin/submodule--helper.c:1859:11
>      #9 0x51e024 in run_builtin /home/jfe/git/git.c:346:11
>      #10 0x5192c2 in handle_builtin /home/jfe/git/git.c:554:8
>      #11 0x51d0f0 in run_argv /home/jfe/git/git.c:606:4
>      #12 0x518600 in cmd_main /home/jfe/git/git.c:683:19
>      #13 0x8501d6 in main /home/jfe/git/common-main.c:43:9
>      #14 0x7f49fdaf2f29 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x20f29)
>      #15 0x41f4b9 in _start (/home/jfe/git/inst/libexec/git-core/git+0x41f4b9)
> 
> AddressSanitizer can not provide additional info.
> SUMMARY: AddressSanitizer: SEGV /home/jfe/git/refs.c:1451:20 in refs_read_raw_ref
> ==63400==ABORTING
> 
> As mentioned above, this bug is triggered by issuing the command
> "git submodule status" while in the attached directory.
> 
> This bug was confirmed on Debian with version 2.16.1 and
> 2.17.0.rc1.35.g90bbd502d as well as on Arch Linux with version 2.16.2
> where further output is given by git:
> 
> /usr/lib/git-core/git-submodule: line 979:  8119 Segmentation fault      (core dumped) git ${wt_prefix:+-C "$wt_prefix"} ${prefix:+--super-prefix "$prefix"} submodule--helper status ${GIT_QUIET:+--quiet} ${cached:+--cached} ${recursive:+--recursive} "$@"
> 

You may have minimized too much.  With the patch below I get:

	fatal: no ref store in submodule 'gnulib'

I guess you'll get a different one in your original repo.

The patch seems like a good idea in any case, though.

-- >8 --
Subject: [PATCH] submodule: check for NULL return of get_submodule_ref_store()

refs_head_ref() requires a valid ref_store pointer to be given as its
first argument.  get_submodule_ref_store() can return NULL.  Exit and
report the failure to find a ref store in that case instead of
segfaulting.

Reported-by: Jeremy Feusi <jeremy@xxxxxxxx>
Signed-off-by: Rene Scharfe <l.s.r@xxxxxx>
---
 builtin/submodule--helper.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index ee020d4749..0f74e81005 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -654,9 +654,11 @@ static void status_submodule(const char *path, const struct object_id *ce_oid,
 			     displaypath);
 	} else if (!(flags & OPT_CACHED)) {
 		struct object_id oid;
+		struct ref_store *refs = get_submodule_ref_store(path);
 
-		if (refs_head_ref(get_submodule_ref_store(path),
-				  handle_submodule_head_ref, &oid))
+		if (!refs)
+			die(_("no ref store in submodule '%s'"), path);
+		if (refs_head_ref(refs, handle_submodule_head_ref, &oid))
 			die(_("could not resolve HEAD ref inside the "
 			      "submodule '%s'"), path);
 
-- 
2.16.3



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