[PATCH v3 04/16] index-helper: add --strict
- From
David Turner <dturner@twopensource.com>
- Date
- Apr 6, 2016, 22:11 UTC
- Message-ID
- <1459980722-4836-5-git-send-email-dturner@twopensource.com>
- In-Reply-To
- <1459980722-4836-1-git-send-email-dturner@twopensource.com>
From: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
There are "holes" in the index-helper approach because the shared memory is not verified again by git. If $USER is compromised, shared memory could be modified. But anyone who could do this could already modify $GIT_DIR/index. A more realistic risk is some bugs in index-helper that produce corrupt shared memory. --strict is added to avoid that.
Strictly speaking there's still a very small gap where corrupt shared memory could still be read by git: after we write the trailing SHA-1 in the shared memory (thus signaling "this shm is ready") and before verify_shm() detects an error.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> --- Documentation/git-index-helper.txt | 9 +++++++ cache.h | 1 + index-helper.c | 48 ++++++++++++++++++++++++++++++++++++++ read-cache.c | 9 ++++--- 4 files changed, 64 insertions(+), 3 deletions(-)
diff --git a/Documentation/git-index-helper.txt b/Documentation/git-index-helper.txt index 61605e9..b177fb8 100644 --- a/Documentation/git-index-helper.txt +++ b/Documentation/git-index-helper.txt @@ -22,6 +22,15 @@ OPTIONS Exit if the cached index is not accessed for `<n>` seconds. Specify 0 to wait forever. Default is 600. +--strict:: +--no-strict:: + Strict mode makes index-helper verify the shared memory after + it's created. If the result does not match what's read from + $GIT_DIR/index, the shared memory is destroyed. This makes + index-helper take more than double the amount of time required + for reading an index, but because it will happen in the + background, it's not noticable. `--strict` is enabled by default. + NOTES ----- $GIT_DIR/index-helper.path is a symlink to a Unix domain socket in diff --git a/cache.h b/cache.h index 43fb314..4b678e9 100644 --- a/cache.h +++ b/cache.h @@ -336,6 +336,7 @@ struct index_state { keep_mmap : 1, from_shm : 1, to_shm : 1, + always_verify_trailing_sha1 : 1, initialized : 1; struct hashmap name_hash; struct hashmap dir_hash; diff --git a/index-helper.c b/index-helper.c index 263b066..8288e30 100644 --- a/index-helper.c +++ b/index-helper.c @@ -15,6 +15,7 @@ struct shm { static struct shm shm_index; static struct shm shm_base_index; +static int to_verify = 1; static void release_index_shm(struct shm *is) { @@ -76,11 +77,56 @@ static void share_index(struct index_state *istate, struct shm *is) hashcpy((unsigned char *)new_mmap + istate->mmap_size - 20, is->sha1); } +static int verify_shm(void) +{ + int i; + struct index_state istate; + memset(&istate, 0, sizeof(istate)); + istate.always_verify_trailing_sha1 = 1; + istate.to_shm = 1; + i = read_index(&istate); + if (i != the_index.cache_nr) + goto done; + for (; i < the_index.cache_nr; i++) { + struct cache_entry *base, *ce; + /* namelen is checked separately */ + const unsigned int ondisk_flags = + CE_STAGEMASK | CE_VALID | CE_EXTENDED_FLAGS; + unsigned int ce_flags, base_flags, ret; + base = the_index.cache[i]; + ce = istate.cache[i]; + if (ce->ce_namelen != base->ce_namelen || + strcmp(ce->name, base->name)) { + warning("mismatch at entry %d", i); + break; + } + ce_flags = ce->ce_flags; + base_flags = base->ce_flags; + /* only on-disk flags matter */ + ce->ce_flags &= ondisk_flags; + base->ce_flags &= ondisk_flags; + ret = memcmp(&ce->ce_stat_data, &base->ce_stat_data, + offsetof(struct cache_entry, name) - + offsetof(struct cache_entry, ce_stat_data)); + ce->ce_flags = ce_flags; + base->ce_flags = base_flags; + if (ret) { + warning("mismatch at entry %d", i); + break; + } + } +done: + discard_index(&istate); + return i == the_index.cache_nr; +} + static void share_the_index(void) { if (the_index.split_index && the_index.split_index->base) share_index(the_index.split_index->base, &shm_base_index); share_index(&the_index, &shm_index); + if (to_verify && !verify_shm()) + cleanup_shm(); discard_index(&the_index); } @@ -249,6 +295,8 @@ int main(int argc, char **argv) struct option options[] = { OPT_INTEGER(0, "exit-after", &idle_in_seconds, N_("exit if not used after some seconds")), + OPT_BOOL(0, "strict", &to_verify, + "verify shared memory after creating"), OPT_END() }; diff --git a/read-cache.c b/read-cache.c index 66f2874..7215a17 100644 --- a/read-cache.c +++ b/read-cache.c @@ -1665,9 +1665,12 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist) istate->mmap = mmap; istate->mmap_size = mmap_size; - if (try_shm(istate) && - verify_hdr(istate->mmap, istate->mmap_size) < 0) - goto unmap; + if (try_shm(istate)) { + if (verify_hdr(istate->mmap, istate->mmap_size) < 0) + goto unmap; + } else if (istate->always_verify_trailing_sha1 && + verify_hdr(istate->mmap, istate->mmap_size) < 0) + goto unmap; hdr = mmap = istate->mmap; mmap_size = istate->mmap_size; if (!istate->keep_mmap)
-- 2.4.2.767.g62658d5-twtrsrc