Libguestfs - Mar 2015 - [PATCH] fuse: resolve absolute links to relative ones

First it strips /sysroot and then finds common prefix aligned
on slashes. Next it produces ../ for each slash found in common
prefix and concatenates them with the rest of resolved link.

Fixes RHBZ#604041

Maros Zatko (1):
  fuse: resolve absolute links to relative ones

 src/fuse.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

-- 
1.9.3

First it strips /sysroot and then finds common prefix aligned
on slashes. Next it produces ../ for each slash found in common
prefix and concatenates them with the rest of resolved link.

Fixes RHBZ#604041
---
 src/fuse.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/fuse.c b/src/fuse.c
index 3fdb1d4..6c7eee1 100644
--- a/src/fuse.c
+++ b/src/fuse.c
@@ -386,7 +386,38 @@ mount_local_readlink (const char *path, char *buf, size_t
size)
   if (len > size - 1)
     len = size - 1;
 
-  memcpy (buf, r, len);
+  buf[0] = '\0';
+  size_t offset = 0;
+  if (STRPREFIX (r, "/sysroot")) {
+    offset = strlen ("/sysroot") + 1;
+    size_t i;
+    for (i = 0; (i < strlen (r+offset)) && (path[i] ==
r[i+offset-1]); i++);
+    /* Now i contains index where paths starts to differ
+     * (n.b. needs to be aligned on last slash). */
+
+    for (; path[i] != '/'; --i);
+    /* i is now aligned */
+
+    /* Count slashes in original path, so we can generate
+     * right amount of ../ */
+    size_t j; int cnt = 0;
+    for (j = i+1; j < strlen (r+offset); j++) {
+      if (path[j] == '/') cnt++;
+    }
+
+    /* For each slash create ../ in path */
+    for (int z = 0; z < cnt; z++) {
+      strcat (buf, "../");
+    }
+
+    /* In addition to /sysroot ne need to remove common path
+     * aligned on slashes */
+    offset += i;
+  }
+
+  /* There might already be something in buf (such as ../)
+   * so let's concatenate the rest of path */
+  strncat (buf, r + offset, len - offset + 1);
   buf[len] = '\0';
 
   if (free_it) {
-- 
1.9.3

On Wed, Mar 18, 2015 at 02:21:31PM +0100, Maros Zatko
wrote:
> First it strips /sysroot and then finds common prefix aligned
> on slashes. Next it produces ../ for each slash found in common
> prefix and concatenates them with the rest of resolved link.
> 
> Fixes RHBZ#604041
> ---
>  src/fuse.c | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/src/fuse.c b/src/fuse.c
> index 3fdb1d4..6c7eee1 100644
> --- a/src/fuse.c
> +++ b/src/fuse.c
> @@ -386,7 +386,38 @@ mount_local_readlink (const char *path, char *buf,
size_t size)
>    if (len > size - 1)
>      len = size - 1;
>  
> -  memcpy (buf, r, len);
> +  buf[0] = '\0';
> +  size_t offset = 0;
> +  if (STRPREFIX (r, "/sysroot")) {
> +    offset = strlen ("/sysroot") + 1;
> +    size_t i;
> +    for (i = 0; (i < strlen (r+offset)) && (path[i] ==
r[i+offset-1]); i++);
> +    /* Now i contains index where paths starts to differ
> +     * (n.b. needs to be aligned on last slash). */
> +
> +    for (; path[i] != '/'; --i);
> +    /* i is now aligned */
> +
> +    /* Count slashes in original path, so we can generate
> +     * right amount of ../ */
> +    size_t j; int cnt = 0;
> +    for (j = i+1; j < strlen (r+offset); j++) {
> +      if (path[j] == '/') cnt++;
> +    }
> +
> +    /* For each slash create ../ in path */
> +    for (int z = 0; z < cnt; z++) {
> +      strcat (buf, "../");
> +    }
> +
> +    /* In addition to /sysroot ne need to remove common path
> +     * aligned on slashes */
> +    offset += i;
> +  }
> +
> +  /* There might already be something in buf (such as ../)
> +   * so let's concatenate the rest of path */
> +  strncat (buf, r + offset, len - offset + 1);
>    buf[len] = '\0';
This makes my head hurt.  Perhaps some diagrams or examples
of how this is supposed to work?

Rich.

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