On Mon, Dec 04, 2023 at 02:39:24PM +0100, Philippe Mathieu-Daudé wrote: > Hi Laurent, Helge, Richard, > > On 1/12/23 19:51, Shu-Chun Weng wrote: > > On Fri, Dec 1, 2023 at 4:42 AM Philippe Mathieu-Daudé <phi...@linaro.org > > <mailto:phi...@linaro.org>> wrote: > > > > Hi Shu-Chun, > > > > On 1/12/23 04:21, Shu-Chun Weng wrote: > > > Commit b8002058 strengthened openat()'s /proc detection by calling > > > realpath(3) on the given path, which allows various paths and > > symlinks > > > that points to the /proc file system to be intercepted correctly. > > > > > > Using realpath(3), though, has a side effect that it reads the > > symlinks > > > along the way, and thus changes their atime. The results in the > > > following code snippet already get ~now instead of the real atime: > > > > > > int fd = open("/path/to/a/symlink", O_PATH | O_NOFOLLOW); > > > struct stat st; > > > fstat(fd, st); > > > return st.st_atime; > > > > > > This change opens a path that doesn't appear to be part of /proc > > > directly and checks the destination of /proc/self/fd/n to > > determine if > > > it actually refers to a file in /proc. > > > > > > Neither this nor the existing code works with symlinks or > > indirect paths > > > (e.g. /tmp/../proc/self/exe) that points to /proc/self/exe > > because it > > > is itself a symlink, and both realpath(3) and /proc/self/fd/n will > > > resolve into the location of QEMU. > > > > Does this fix any of the following issues? > > https://gitlab.com/qemu-project/qemu/-/issues/829 > > <https://gitlab.com/qemu-project/qemu/-/issues/829> > > > > > > Not this one -- this is purely in the logic of util/path.c, which we do > > see and carry an internal patch. It's quite a behavior change so we > > never upstreamed it. > > > > https://gitlab.com/qemu-project/qemu/-/issues/927 > > <https://gitlab.com/qemu-project/qemu/-/issues/927> > > > > > > No, either. This patch only touches the path handling, not how files are > > opened. > > > > https://gitlab.com/qemu-project/qemu/-/issues/2004 > > <https://gitlab.com/qemu-project/qemu/-/issues/2004> > > > > > > Yes! Though I don't have a toolchain for HPPA or any of the > > architectures intercepting /proc/cpuinfo handy, I hacked the condition > > and confirmed that on 7.1 and 8.2, test.c as attached in the bug prints > > out the host cpuinfo while with this patch, it prints out the content > > generated by `open_cpuinfo()`. > > > > > > > > > Signed-off-by: Shu-Chun Weng <s...@google.com > > <mailto:s...@google.com>> > > > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2004 > > <https://gitlab.com/qemu-project/qemu/-/issues/2004> > > Do we need to merge this for 8.2?
Please assign release blocker issues to the 8.2 milestone so that are tracked: https://gitlab.com/qemu-project/qemu/-/milestones/10 Thanks, Stefan > > > > > > --- > > > linux-user/syscall.c | 42 > > +++++++++++++++++++++++++++++++++--------- > > > 1 file changed, 33 insertions(+), 9 deletions(-) > > > > > > On Fri, Dec 1, 2023 at 9:09 AM Helge Deller <del...@gmx.de > > <mailto:del...@gmx.de>> wrote: > > > > On 12/1/23 04:21, Shu-Chun Weng wrote: > > > Commit b8002058 strengthened openat()'s /proc detection by calling > > > realpath(3) on the given path, which allows various paths and > > symlinks > > > that points to the /proc file system to be intercepted correctly. > > > > > > Using realpath(3), though, has a side effect that it reads the > > symlinks > > > along the way, and thus changes their atime. > > > > Ah, ok. I didn't thought of that side effect when I came up with the > > patch. > > Does the updated atimes trigger some real case issue ? > > > > > > We have an internal library shimming the underlying filesystem that uses > > the `open(O_PATH|O_NOFOLLOW)`+`fstat()` pattern for all file stats. > > Checking symlink atime is in one of the unittests, though I don't know > > if production ever uses it. > > > > > > Helge > > >
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