[FFmpeg-devel] [PATCH v3 1/2] avformat/url: fix logic for removing ".." path components

[Zlomek, Josef]

see version 3

On Tue, Jul 28, 2020 at 12:37 PM Steven Liu <lingjiujianke at gmail.com> wrote:

> Josef Zlomek <josef at pex.com> 于2020年7月28日周二 下午12:11写道：
> >
> > Fixes: 8814
> >
> > The logic for removing ".." path components and their corresponding
> > upper directories was reworked.
> >
> > Now, the function trim_double_dot_url splits the path by "/" into
> > components, and processes the components one ny one:
> > - if the component is "..", the last path component in output buffer is
> removed
> > - if the component is not empty, it is added to the output buffer
> > No temporary buffers are used anymore.
> >
> > Also the path containing no '/' after '://' is returned as it is.
> >
> > The duplicate logic was removed from ff_make_absolute_url.
> >
> > Signed-off-by: Josef Zlomek <josef at pex.com>
> > ---
> >  libavformat/url.c | 101 +++++++++++++++++++++++-----------------------
> >  1 file changed, 50 insertions(+), 51 deletions(-)
> >
> > diff --git a/libavformat/url.c b/libavformat/url.c
> > index 20463a6674..46a08e88e3 100644
> > --- a/libavformat/url.c
> > +++ b/libavformat/url.c
> > @@ -82,41 +82,62 @@ static void trim_double_dot_url(char *buf, const
> char *rel, int size)
> >  {
> >      const char *p = rel;
> >      const char *root = rel;
> > -    char tmp_path[MAX_URL_SIZE] = {0, };
> > -    char *sep;
> > -    char *node;
> > +    char *dst;
> > +    int dst_len = 0;
> > +    const char *sep;
> > +    const char *next;
> > +    int last_is_dir;
> >
> >      /* Get the path root of the url which start by "://" */
> >      if (p && (sep = strstr(p, "://"))) {
> >          sep += 3;
> >          root = strchr(sep, '/');
> > -        if (!root)
> > +        if (!root) {
> > +            av_strlcpy(buf, rel, size);
> >              return;
> > +        }
> >      }
> > +    if (*root == '/')
> > +        ++root;
> >
> > -    /* set new current position if the root node is changed */
> > -    p = root;
> > -    while (p && (node = strstr(p, ".."))) {
> > -        av_strlcat(tmp_path, p, node - p + strlen(tmp_path));
> > -        p = node + 3;
> > -        sep = strrchr(tmp_path, '/');
> > -        if (sep)
> > -            sep[0] = '\0';
> > -        else
> > -            tmp_path[0] = '\0';
> > -    }
> > -
> > -    if (!av_stristart(p, "/", NULL) && root != rel)
> > -        av_strlcat(tmp_path, "/", size);
> > -
> > -    av_strlcat(tmp_path, p, size);
> > -    /* start set buf after temp path process. */
> > +    /* Copy the root to the output buffer */
> >      av_strlcpy(buf, rel, root - rel + 1);
> > +    size -= root - rel;
> > +    dst = &buf[root - rel];
> > +
> > +    /* Split the path by "/" and remove ".." and its corresponding
> directory. */
> > +    last_is_dir = 1;
> > +    for (p = root; *p; p = next) {
> > +        next = strchr(p, '/');
> > +        if (!next) {
> > +            next = p + strlen(p);
> > +            last_is_dir = 0;
> > +        }
> >
> > -    if (!av_stristart(tmp_path, "/", NULL) && root != rel)
> > -        av_strlcat(buf, "/", size);
> > +        if (next - p == 2 && !strncmp(p, "..", 2)) {
> > +            /* remove the last directory from dst */
> > +            while (dst_len > 0 && dst[--dst_len] != '/')
> > +                ;
> > +            dst[dst_len] = '\0';
> > +            last_is_dir = 1;
> > +        } else if (next > p) {
> > +            int len_including_zero;
> > +            /* copy the current path component to dst (including '/') */
> > +            if (dst_len) {
> > +                av_strlcpy(dst + dst_len, "/", size - dst_len);
> > +                ++dst_len;
> > +            }
> > +            len_including_zero = FFMIN(size - dst_len, next - p + 1);
> > +            av_strlcpy(dst + dst_len, p, len_including_zero);
> > +            dst_len += len_including_zero - 1;
> > +        }
> >
> > -    av_strlcat(buf, tmp_path, size);
> > +        /* skip "/" */
> > +        while (*next == '/')
> > +            ++next;
> > +    }
> > +    if (last_is_dir && dst_len)
> > +        av_strlcpy(dst + dst_len, "/", size - dst_len);
> >  }
> >
> >  void ff_make_absolute_url(char *buf, int size, const char *base,
> > @@ -175,14 +196,11 @@ void ff_make_absolute_url(char *buf, int size,
> const char *base,
> >
> >      root = p = buf;
> >      /* Get the path root of the url which start by "://" */
> > -    if (p && strstr(p, "://")) {
> > -        sep = strstr(p, "://");
> > -        if (sep) {
> > -            sep += 3;
> > -            root = strchr(sep, '/');
> > -            if (!root)
> > -                return;
> > -        }
> > +    if (p && (sep = strstr(p, "://"))) {
> > +        sep += 3;
> > +        root = strchr(sep, '/');
> > +        if (!root)
> > +            return;
> >      }
> >
> >      /* Remove the file name from the base url */
> > @@ -194,26 +212,7 @@ void ff_make_absolute_url(char *buf, int size,
> const char *base,
> >          sep[1] = '\0';
> >      else
> >          buf[0] = '\0';
> > -    while (av_strstart(rel, "..", NULL) && sep) {
> > -        /* Remove the path delimiter at the end */
> > -        if (sep > root) {
> > -            sep[0] = '\0';
> > -            sep = strrchr(buf, '/');
> > -        }
> >
> > -        /* If the next directory name to pop off is "..", break here */
> > -        if (!strcmp(sep ? &sep[1] : buf, "..")) {
> > -            /* Readd the slash we just removed */
> > -            av_strlcat(buf, "/", size);
> > -            break;
> > -        }
> > -        /* Cut off the directory name */
> > -        if (sep)
> > -            sep[1] = '\0';
> > -        else
> > -            buf[0] = '\0';
> > -        rel += 3;
> > -    }
> >      av_strlcat(buf, rel, size);
> >      trim_double_dot_url(tmp_path, buf, size);
> As Marton said, tmp_path should remove too.
>
> >      memset(buf, 0, size);
> > --
> > 2.17.1
> >
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-- 
Josef Zlomek