# [PATCH] read-cache.c: do not die if mmap fails 2 messages from 2019-07-14 to 2019-07-14. Participants: Varun Naik, Junio C Hamano. Thread: https://gitlist.dev/t/51480 ## Varun Naik, 2019-07-14 03:01 Subject: [PATCH] read-cache.c: do not die if mmap fails Message-ID: <20190714030153.22022-1-vcnaik94@gmail.com> URL: https://gitlist.dev/e/20190714030153.22022-1-vcnaik94%40gmail.com ``` do_read_index() mmaps the index, or tries to die with an error message on failure. It should call xmmap_gently(), which returns MAP_FAILED, rather than xmmap(), which dies with its own error message. An easy way to cause this mmap to fail is by setting $GIT_INDEX_FILE to a path to a directory and then invoking any command that reads from the index. Signed-off-by: Varun Naik --- I believe this is the only place that calls xmmap() when it should be calling xmmap_gently(). There is a related recent commit 3203566a71 ("Use xmmap_gently instead of xmmap in use_pack", 2019-05-16). read-cache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/read-cache.c b/read-cache.c index 22e7b9944e..4e30dafa9d 100644 --- a/read-cache.c +++ b/read-cache.c @@ -2140,7 +2140,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist) if (mmap_size < sizeof(struct cache_header) + the_hash_algo->rawsz) die(_("%s: index file smaller than expected"), path); - mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0); + mmap = xmmap_gently(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0); if (mmap == MAP_FAILED) die_errno(_("%s: unable to map index file"), path); close(fd); -- 2.22.0 ``` ## Junio C Hamano, 2019-07-14 18:59 Subject: Re: [PATCH] read-cache.c: do not die if mmap fails Message-ID: URL: https://gitlist.dev/e/xmqq7e8k5tn9.fsf%40gitster-ct.c.googlers.com In-Reply-To: <20190714030153.22022-1-vcnaik94@gmail.com> ``` Varun Naik writes: > do_read_index() mmaps the index, or tries to die with an error message > on failure. It should call xmmap_gently(), which returns MAP_FAILED, > rather than xmmap(), which dies with its own error message. > > An easy way to cause this mmap to fail is by setting $GIT_INDEX_FILE to > a path to a directory and then invoking any command that reads from the > index. > > Signed-off-by: Varun Naik > --- > I believe this is the only place that calls xmmap() when it should be > calling xmmap_gently(). There is a related recent commit 3203566a71 > ("Use xmmap_gently instead of xmmap in use_pack", 2019-05-16). Nice find and thanks for checking other callsites of xmmap(). > > read-cache.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/read-cache.c b/read-cache.c > index 22e7b9944e..4e30dafa9d 100644 > --- a/read-cache.c > +++ b/read-cache.c > @@ -2140,7 +2140,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist) > if (mmap_size < sizeof(struct cache_header) + the_hash_algo->rawsz) > die(_("%s: index file smaller than expected"), path); > > - mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0); > + mmap = xmmap_gently(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0); > if (mmap == MAP_FAILED) > die_errno(_("%s: unable to map index file"), path); > close(fd); ```