# Segfault in git_config_set_multivar_in_file_gently with direct_io in FUSE filesystem 7 messages from 2016-12-16 to 2016-12-20. Participants: Josh Bleecher Snyder, Nguyễn Thái Ngọc Duy, Junio C Hamano, Duy Nguyen. Thread: https://gitlist.dev/t/44717 ## Josh Bleecher Snyder, 2016-12-16 18:41 Subject: Segfault in git_config_set_multivar_in_file_gently with direct_io in FUSE filesystem Message-ID: URL: https://gitlist.dev/e/CAFAcib_cY8FeLFkW1%3DMfR%2BP7xoupGK9DFegNY5boExHSRppAmg%40mail.gmail.com ``` I am using git with a simple in-memory FUSE filesystem. When I enable direct_io, I get a segfault from git_config_set_multivar_in_file_gently during git clone. I have full reproduction instructions using Go and macOS at https://github.com/josharian/gitbug. It also includes a stack trace in case anyone wants to try blind debugging. Happy to provide more info if it will help. Thanks, Josh ``` ## Nguyễn Thái Ngọc Duy, 2016-12-19 09:21 Subject: [PATCH] config.c: handle error case for fstat() calls Message-ID: <20161219092155.20359-1-pclouds@gmail.com> URL: https://gitlist.dev/e/20161219092155.20359-1-pclouds%40gmail.com In-Reply-To: ``` Signed-off-by: Nguyễn Thái Ngọc Duy --- Will this fix the problem I'm replying to? I don't know. I found this while checking the code and it should be fixed regardless. config.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/config.c b/config.c index 83fdecb..4973256 100644 --- a/config.c +++ b/config.c @@ -2194,7 +2194,12 @@ int git_config_set_multivar_in_file_gently(const char *config_filename, goto out_free; } - fstat(in_fd, &st); + if (fstat(in_fd, &st) == -1) { + error_errno(_("fstat on %s failed"), config_filename); + ret = CONFIG_INVALID_FILE; + goto out_free; + } + contents_sz = xsize_t(st.st_size); contents = xmmap_gently(NULL, contents_sz, PROT_READ, MAP_PRIVATE, in_fd, 0); @@ -2414,7 +2419,10 @@ int git_config_rename_section_in_file(const char *config_filename, goto unlock_and_out; } - fstat(fileno(config_file), &st); + if (fstat(fileno(config_file), &st) == -1) { + ret = error_errno(_("fstat on %s failed"), config_filename); + goto out; + } if (chmod(get_lock_file_path(lock), st.st_mode & 07777) < 0) { ret = error_errno("chmod on %s failed", -- 2.8.2.524.g6ff3d78 ``` ## Junio C Hamano, 2016-12-19 18:14 Subject: Re: [PATCH] config.c: handle error case for fstat() calls Message-ID: URL: https://gitlist.dev/e/xmqqtw9zpz0c.fsf%40gitster.mtv.corp.google.com In-Reply-To: <20161219092155.20359-1-pclouds@gmail.com> ``` Nguyễn Thái Ngọc Duy writes: > Signed-off-by: Nguyễn Thái Ngọc Duy > --- > Will this fix the problem I'm replying to? I don't know. I found this > while checking the code and it should be fixed regardless. Yeah, from a cursory read, it is a step in the right direction to check the return value of fstat(). Shouldn't the error-return path in the second hunk rollback the lockfile to clean after itself? The existing "Oh, we cannot chmod to match the original" check that comes immediately after shares the same issue, so this is not a new problem, but making an existing one worse. > config.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/config.c b/config.c > index 83fdecb..4973256 100644 > --- a/config.c > +++ b/config.c > @@ -2194,7 +2194,12 @@ int git_config_set_multivar_in_file_gently(const char *config_filename, > goto out_free; > } > > - fstat(in_fd, &st); > + if (fstat(in_fd, &st) == -1) { > + error_errno(_("fstat on %s failed"), config_filename); > + ret = CONFIG_INVALID_FILE; > + goto out_free; > + } > + > contents_sz = xsize_t(st.st_size); > contents = xmmap_gently(NULL, contents_sz, PROT_READ, > MAP_PRIVATE, in_fd, 0); > @@ -2414,7 +2419,10 @@ int git_config_rename_section_in_file(const char *config_filename, > goto unlock_and_out; > } > > - fstat(fileno(config_file), &st); > + if (fstat(fileno(config_file), &st) == -1) { > + ret = error_errno(_("fstat on %s failed"), config_filename); > + goto out; > + } > > if (chmod(get_lock_file_path(lock), st.st_mode & 07777) < 0) { > ret = error_errno("chmod on %s failed", ``` ## Duy Nguyen, 2016-12-20 09:47 Subject: Re: [PATCH] config.c: handle error case for fstat() calls Message-ID: <20161220094746.GA3917@ash> URL: https://gitlist.dev/e/20161220094746.GA3917%40ash In-Reply-To: ``` On Mon, Dec 19, 2016 at 10:14:27AM -0800, Junio C Hamano wrote: > Shouldn't the error-return path in the second hunk rollback the > lockfile to clean after itself? The existing "Oh, we cannot chmod > to match the original" check that comes immediately after shares the > same issue, so this is not a new problem, but making an existing one > worse. OK. How about two more patches on top (or bottom, does not matter)? The second one should fix this. The first is sort of "good to do". [PATCH 1/2] config.c: rename label unlock_and_out [PATCH 2/2] config.c: handle lock file in error case in git_config_rename_... -- Duy ``` ## Nguyễn Thái Ngọc Duy, 2016-12-20 09:48 Subject: [PATCH 1/2] config.c: rename label unlock_and_out Message-ID: <20161220094836.4131-1-pclouds@gmail.com> URL: https://gitlist.dev/e/20161220094836.4131-1-pclouds%40gmail.com In-Reply-To: <20161220094746.GA3917@ash> ``` There are two ways to unlock a file: commit, or revert. Rename it to commit_and_out to avoid confusion. Signed-off-by: Nguyễn Thái Ngọc Duy --- config.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/config.c b/config.c index 4973256..505e0d0 100644 --- a/config.c +++ b/config.c @@ -2416,7 +2416,7 @@ int git_config_rename_section_in_file(const char *config_filename, if (!(config_file = fopen(config_filename, "rb"))) { /* no config file means nothing to rename, no error */ - goto unlock_and_out; + goto commit_and_out; } if (fstat(fileno(config_file), &st) == -1) { @@ -2478,7 +2478,7 @@ int git_config_rename_section_in_file(const char *config_filename, } } fclose(config_file); -unlock_and_out: +commit_and_out: if (commit_lock_file(lock) < 0) ret = error_errno("could not write config file %s", config_filename); -- 2.8.2.524.g6ff3d78 ``` ## Nguyễn Thái Ngọc Duy, 2016-12-20 09:48 Subject: [PATCH 2/2] config.c: handle lock file in error case in git_config_rename_... Message-ID: <20161220094836.4131-2-pclouds@gmail.com> URL: https://gitlist.dev/e/20161220094836.4131-2-pclouds%40gmail.com In-Reply-To: <20161220094836.4131-1-pclouds@gmail.com> ``` We could rely on atexit() to clean up everything, but let's be explicit when we can. And it's good anyway because the function is called the second time in the same process, we're in trouble. This function should not affect the successful case because after commit_lock_file() is called, rollback_lock_file() becomes no-op. Signed-off-by: Nguyễn Thái Ngọc Duy --- config.c | 1 + 1 file changed, 1 insertion(+) diff --git a/config.c b/config.c index 505e0d0..e02def4 100644 --- a/config.c +++ b/config.c @@ -2483,6 +2483,7 @@ int git_config_rename_section_in_file(const char *config_filename, ret = error_errno("could not write config file %s", config_filename); out: + rollback_lock_file(lock); free(filename_buf); return ret; } -- 2.8.2.524.g6ff3d78 ``` ## Junio C Hamano, 2016-12-20 20:09 Subject: Re: [PATCH 2/2] config.c: handle lock file in error case in git_config_rename_... Message-ID: URL: https://gitlist.dev/e/xmqqfulijrah.fsf%40gitster.mtv.corp.google.com In-Reply-To: <20161220094836.4131-2-pclouds@gmail.com> ``` Nguyễn Thái Ngọc Duy writes: > We could rely on atexit() to clean up everything, but let's be > explicit when we can. And it's good anyway because the function is > called the second time in the same process, we're in trouble. > > This function should not affect the successful case because after > commit_lock_file() is called, rollback_lock_file() becomes no-op. Not really. At the point of the first "goto out" in this function, lock is merely an uninitialized pointer. > > Signed-off-by: Nguyễn Thái Ngọc Duy > --- > config.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/config.c b/config.c > index 505e0d0..e02def4 100644 > --- a/config.c > +++ b/config.c > @@ -2483,6 +2483,7 @@ int git_config_rename_section_in_file(const char *config_filename, > ret = error_errno("could not write config file %s", > config_filename); > out: > + rollback_lock_file(lock); > free(filename_buf); > return ret; > } ```