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Date: Fri, 28 Mar 2025 15:29:10 +0100
From: Stefano Brivio <sbrivio@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH v2] pasta, passt-repair: Support multiple events per
read() in inotify handlers
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On Fri, 28 Mar 2025 11:39:58 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:
> From: Stefano Brivio <sbrivio@redhat.com>
>
> The current code assumes that we'll get one event per read() on
> inotify descriptors, but that's not the case, not from documentation,
> and not from reports.
>
> Add loops in the two inotify handlers we have, in pasta-specific code
> and passt-repair, to go through all the events we receive.
>
> Link: https://bugs.passt.top/show_bug.cgi?id=119
>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> [dwg: Remove unnecessary buffer expansion, use strnlen instead of strlen
> to make Coverity happier]
I have to admit I didn't know about strnlen(). POSIX.1-2008, that's
bleeding edge stuff. :)
That wasn't actually enough though: in my Coverity scan, it was also
complaining about:
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> passt-repair.c | 27 ++++++++++++++++++++-------
> pasta.c | 20 +++++++++++++-------
> 2 files changed, 33 insertions(+), 14 deletions(-)
>
> diff --git a/passt-repair.c b/passt-repair.c
> index 120f7aa7..d36c9c94 100644
> --- a/passt-repair.c
> +++ b/passt-repair.c
> @@ -111,14 +111,14 @@ int main(int argc, char **argv)
> }
>
> if ((sb.st_mode & S_IFMT) == S_IFDIR) {
> - char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
> + char buf[sizeof(struct inotify_event) + NAME_MAX + 1]
> + __attribute__ ((aligned(__alignof__(struct inotify_event))));
> const struct inotify_event *ev;
> char path[PATH_MAX + 1];
> + bool found = false;
> ssize_t n;
> int fd;
>
> - ev = (struct inotify_event *)buf;
> -
> if ((fd = inotify_init1(IN_CLOEXEC)) < 0) {
> fprintf(stderr, "inotify_init1: %i\n", errno);
> _exit(1);
> @@ -130,6 +130,8 @@ int main(int argc, char **argv)
> }
>
> do {
> + char *p;
> +
> n = read(fd, buf, sizeof(buf));
> if (n < 0) {
> fprintf(stderr, "inotify read: %i", errno);
> @@ -138,11 +140,22 @@ int main(int argc, char **argv)
>
> if (n < (ssize_t)sizeof(*ev)) {
> fprintf(stderr, "Short inotify read: %zi", n);
> - _exit(1);
> + continue;
> + }
> +
> + for (p = buf; p < buf + n; p += sizeof(*ev) + ev->len) {
> + ev = (const struct inotify_event *)p;
> +
> + if (ev->len >= REPAIR_EXT_LEN &&
> + !memcmp(ev->name +
> + strnlen(ev->name, ev->len) -
> + REPAIR_EXT_LEN,
> + REPAIR_EXT, REPAIR_EXT_LEN)) {
> + found = true;
> + break;
> + }
> }
> - } while (ev->len < REPAIR_EXT_LEN ||
> - memcmp(ev->name + strlen(ev->name) - REPAIR_EXT_LEN,
> - REPAIR_EXT, REPAIR_EXT_LEN));
> + } while (!found);
>
> snprintf(path, sizeof(path), "%s/%s", argv[1], ev->name);
...ev->name not being necessarily NULL-terminated and passed to
snprintf() here. So I applied this with an additional (and useless, unless
the kernel is unrealistically buggy):
if (ev->len > NAME_MAX + 1 || ev->name[ev->len] != '\0') {
fprintf(stderr, "Invalid filename from inotify\n");
_exit(1);
}
--
Stefano