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Re: [PATCH 1/2] linux-user: Fix openat() emulation to correctly detect a
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH 1/2] linux-user: Fix openat() emulation to correctly detect accesses to /proc |
Date: |
Tue, 1 Aug 2023 22:27:03 +0100 |
User-agent: |
Mutt/2.2.9 (2022-11-12) |
On Tue, Aug 01, 2023 at 09:10:34PM +0200, Helge Deller wrote:
> In qemu we catch accesses to files like /proc/cpuinfo or /proc/net/route
> and return to the guest contents which would be visible on a real system
> (instead what the host would show).
>
> This patch fixes a bug, where for example the accesses
> cat /proc////cpuinfo
> or
> cd /proc && cat cpuinfo
> will not be recognized by qemu and where qemu will wrongly show
> the contents of the host's /proc/cpuinfo file.
>
> Signed-off-by: Helge Deller <deller@gmx.de>
>
> --
> v2:
> - use g_autofree instead of pathname on stack
> Daniel P. Berrangé requested to not put buffers on stack.
> Using g_autofree keeps code much cleaner than using
> extended semantics of realpath(), unless I can use g_autofree
> on malloced area from realpath().
g_autofree is backed by free(), so it is fine to use that
with the realpath() allocated buffer.
> ---
> linux-user/syscall.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 95727a816a..a089463969 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -8539,9 +8539,12 @@ static int open_hardware(CPUArchState *cpu_env, int fd)
> }
> #endif
>
> -int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname,
> +
> +int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *fname,
> int flags, mode_t mode, bool safe)
> {
> + g_autofree char *proc_name = g_new(char, PATH_MAX);
> + const char *pathname;
> struct fake_open {
> const char *filename;
> int (*fill)(CPUArchState *cpu_env, int fd);
> @@ -8567,6 +8570,13 @@ int do_guest_openat(CPUArchState *cpu_env, int dirfd,
> const char *pathname,
> { NULL, NULL, NULL }
> };
>
> + /* if this is a file from /proc/ filesystem, expand full name */
> + if (realpath(fname, proc_name) && strncmp(proc_name, "/proc/", 6) == 0) {
> + pathname = proc_name;
> + } else {
> + pathname = fname;
> + }
> +
> if (is_proc_myself(pathname, "exe")) {
> if (safe) {
> return safe_openat(dirfd, exec_path, flags, mode);
> --
> 2.41.0
>
With regards,
Daniel
--
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