kernel/git - git - PowerEL Git System

Author	SHA1	Message	Date
Ævar Arnfjörð Bjarmason	2d3491b117	tr2: log N parent process names on Linux In `2f732bf15e` (tr2: log parent process name, 2021-07-21) we started logging parent process names, but only logged all parents on Windows. on Linux only the name of the immediate parent process was logged. Extend the functionality added there to also log full parent chain on Linux. This requires us to lookup "/proc/<getppid()>/stat" instead of "/proc/<getppid()>/comm". The "comm" file just contains the name of the process, but the "stat" file has both that information, and the parent PID of that process, see procfs(5). We parse out the parent PID of our own parent, and recursively walk the chain of "/proc//stat" files all the way up the chain. A parent PID of 0 indicates the end of the chain. It's possible given the semantics of Linux's PID files that we end up getting an entirely nonsensical chain of processes. It could happen if e.g. we have a chain of processes like: 1 (init) => 321 (bash) => 123 (git) Let's assume that "bash" was started a while ago, and that as shown the OS has already cycled back to using a lower PID for us than our parent process. In the time it takes us to start up and get to trace2_collect_process_info(TRACE2_PROCESS_INFO_STARTUP) our parent process might exit, and be replaced by an entirely different process! We'd racily look up our own getppid(), but in the meantime our parent would exit, and Linux would have cycled all the way back to starting an entirely unrelated process as PID 321. If that happens we'll just silently log incorrect data in our ancestry chain. Luckily we don't need to worry about this except in this specific cycling scenario, as Linux does not have PID randomization. It appears it once did through a third-party feature, but that it was removed around 2006[1]. For anyone worried about this edge case raising PID_MAX via "/proc/sys/kernel/pid_max" will mitigate it, but not eliminate it. One thing we don't need to worry about is getting into an infinite loop when walking "/proc//stat". See `353d3d77f4` (trace2: collect Windows-specific process information, 2019-02-22) for the related Windows code that needs to deal with that, and [2] for an explanation of that edge case. Aside from potential race conditions it's also a bit painful to correctly parse the process name out of "/proc/*/stat". A simpler approach is to use fscanf(), see [3] for an implementation of that, but as noted in the comment being added here it would fail in the face of some weird process names, so we need our own parse_proc_stat() to parse it out. With this patch the "ancestry" chain for a trace2 event might look like this: $ GIT_TRACE2_EVENT=/dev/stdout ~/g/git/git version \| grep ancestry \| jq -r .ancestry [ "bash", "screen", "systemd" ] And in the case of naughty process names like the following. This uses perl's ability to use prctl(PR_SET_NAME, ...). See Perl/perl5@7636ea95c5 (Set the legacy process name with prctl() on assignment to $0 on Linux, 2010-04-15)[4]: $ perl -e '$0 = "(naughty\nname)"; system "GIT_TRACE2_EVENT=/dev/stdout ~/g/git/git version"' \| grep ancestry \| jq -r .ancestry [ "sh", "(naughty\nname)", "bash", "screen", "systemd" ] 1. https://grsecurity.net/news#grsec2110 2. https://lore.kernel.org/git/48a62d5e-28e2-7103-a5bb-5db7e197a4b9@jeffhostetler.com/ 3. https://lore.kernel.org/git/87o8agp29o.fsf@evledraar.gmail.com/ 4. `7636ea95c5` Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago
Ævar Arnfjörð Bjarmason	326460a870	tr2: do compiler enum check in trace2_collect_process_info() Change code added in `2f732bf15e` (tr2: log parent process name, 2021-07-21) to use a switch statement without a "default" branch to have the compiler error if this code ever drifts out of sync with the members of the "enum trace2_process_info_reason". Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago
Ævar Arnfjörð Bjarmason	6eccfc3adf	tr2: leave the parent list empty upon failure & don't leak memory In a subsequent commit I'll be replacing most of this code to log N parents, but let's first fix bugs introduced in the recent `2f732bf15e` (tr2: log parent process name, 2021-07-21). It was using the strbuf_read_file() in the wrong way, its return value is either a length or a negative value on error. If we didn't have a procfs, or otherwise couldn't access it we'd end up pushing an empty string to the trace2 ancestry array. It was also using the strvec_push() API the wrong way. That API always does an xstrdup(), so by detaching the strbuf here we'd leak memory. Let's instead pass in our pointer for strvec_push() to xstrdup(), and then free our own strbuf. I do have some WIP changes to make strvec_push_nodup() non-static, which makes this and some other callsites nicer, but let's just follow the prevailing pattern of using strvec_push() for now. We'll also need to free that "procfs_path" strbuf whether or not strbuf_read_file() succeeds, which was another source of memory leaks in `2f732bf15e`, i.e. we'd leak that memory as well if we weren't on a system where we could read the file from procfs. Let's move all the freeing of the memory to the end of the function. If we're still at STRBUF_INIT with "name" due to not having taken the branch where the strbuf_read_file() succeeds freeing it is redundant. So we could move it into the body of the "if", but just handling freeing the same way for all branches of the function makes it more readable. In combination with the preceding commit this makes all of t[0-9]trace2.sh pass under SANITIZE=leak on Linux. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago
Ævar Arnfjörð Bjarmason	f2cc8881d7	tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Rewrite a comment added in `2f732bf15e` (tr2: log parent process name, 2021-07-21) to describe what we might do under TRACE2_PROCESS_INFO_EXIT in the future, instead of vaguely referring to "something extra". Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago
Ævar Arnfjörð Bjarmason	7d9c80f626	tr2: remove NEEDSWORK comment for "non-procfs" implementations I'm fairly sure that there is no way on Linux to inspect the process tree without using procfs, any tool such as ps(1), top(1) etc. that shows this sort of information ultimately looks the information up in procfs. So let's remove this comment added in `2f732bf15e` (tr2: log parent process name, 2021-07-21), it's setting us up for an impossible task. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago
Emily Shaffer	2f732bf15e	tr2: log parent process name It can be useful to tell who invoked Git - was it invoked manually by a user via CLI or script? By an IDE? In some cases - like 'repo' tool - we can influence the source code and set the GIT_TRACE2_PARENT_SID environment variable from the caller process. In 'repo''s case, that parent SID is manipulated to include the string "repo", which means we can positively identify when Git was invoked by 'repo' tool. However, identifying parents that way requires both that we know which tools invoke Git and that we have the ability to modify the source code of those tools. It cannot scale to keep up with the various IDEs and wrappers which use Git, most of which we don't know about. Learning which tools and wrappers invoke Git, and how, would give us insight to decide where to improve Git's usability and performance. Unfortunately, there's no cross-platform reliable way to gather the name of the parent process. If procfs is present, we can use that; otherwise we will need to discover the name another way. However, the process ID should be sufficient to look up the process name on most platforms, so that code may be shareable. Git for Windows gathers similar information and logs it as a "data_json" event. However, since "data_json" has a variable format, it is difficult to parse effectively in some languages; instead, let's pursue a dedicated "cmd_ancestry" event to record information about the ancestry of the current process and a consistent, parseable way. Git for Windows also gathers information about more than one generation of parent. In Linux further ancestry info can be gathered with procfs, but it's unwieldy to do so. In the interest of later moving Git for Windows ancestry logging to the 'cmd_ancestry' event, and in the interest of later adding more ancestry to the Linux implementation - or of adding this functionality to other platforms which have an easier time walking the process tree - let's make 'cmd_ancestry' accept an array of parentage. Signed-off-by: Emily Shaffer <emilyshaffer@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	3 years ago