2014-09-17 23:48:44

by Todd Vierling

Subject: [PATCH] exportfs: Properly parse IPv6 literal strings with null termination

The original implementation was using strncpy() with a truncation
length to an uninitialized stack buffer, leaving a string that
was only null terminated by luck.

While here, change to use no-copy semantics (no extra buffer) to
avoid buffer overflows altogether.
---
utils/exportfs/exportfs.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index e7d1ac8..bdea12b 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -351,16 +351,15 @@ static int exportfs_generic(char *arg, char *options, int verbose)

static int exportfs_ipv6(char *arg, char *options, int verbose)
{
- char *path, *c, hname[NI_MAXHOST + strlen("/128")];
+ char *path, *c;

arg++;
c = strchr(arg, ']');
if (c == NULL)
return 1;
- strncpy(hname, arg, c - arg);

/* no colon means this is a wildcarded DNS hostname */
- if (strchr(hname, ':') == NULL)
+ if (memchr(arg, ':', c - arg) == NULL)
return exportfs_generic(--arg, options, verbose);

path = strstr(c, ":/");
@@ -370,9 +369,9 @@ static int exportfs_ipv6(char *arg, char *options, int verbose)

/* if there's anything between the closing brace and the
* path separator, it's probably a prefix length */
- strcat(hname, ++c);
+ memmove(c, c + 1, path - c);

- exportfs_parsed(hname, path, options, verbose);
+ exportfs_parsed(arg, path, options, verbose);
return 0;
}

@@ -458,16 +457,15 @@ static int unexportfs_generic(char *arg, int verbose)

static int unexportfs_ipv6(char *arg, int verbose)
{
- char *path, *c, hname[NI_MAXHOST + strlen("/128")];
+ char *path, *c;

arg++;
c = strchr(arg, ']');
if (c == NULL)
return 1;
- strncpy(hname, arg, c - arg);

/* no colon means this is a wildcarded DNS hostname */
- if (strchr(hname, ':') == NULL)
+ if (memchr(arg, ':', c - arg) == NULL)
return unexportfs_generic(--arg, verbose);

path = strstr(c, ":/");
@@ -477,9 +475,9 @@ static int unexportfs_ipv6(char *arg, int verbose)

/* if there's anything between the closing brace and the
* path separator, it's probably a prefix length */
- strcat(hname, ++c);
+ memmove(c, c + 1, path - c);

- unexportfs_parsed(hname, path, verbose);
+ unexportfs_parsed(arg, path, verbose);
return 0;
}

--
1.8.3.1

2014-09-18 16:52:31

by Chuck Lever

Subject: Re: [PATCH] exportfs: Properly parse IPv6 literal strings with null termination

Thanks for chasing this down, Todd!

On Sep 17, 2014, at 4:48 PM, Todd Vierling <[email protected]> wrote:

> The original implementation was using strncpy() with a truncation
> length to an uninitialized stack buffer, leaving a string that
> was only null terminated by luck.
>
> While here, change to use no-copy semantics (no extra buffer) to
> avoid buffer overflows altogether.

Needs

Fixes: 4663c648 (exportfs: Support raw IPv6 addresses with "client:/path?)

And needs a Signed-off-by.

I wonder about the ?no-copy? change. I thought that on some systems,
the tool chain makes the command line arguments read-only.

> ---
> utils/exportfs/exportfs.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
> index e7d1ac8..bdea12b 100644
> --- a/utils/exportfs/exportfs.c
> +++ b/utils/exportfs/exportfs.c
> @@ -351,16 +351,15 @@ static int exportfs_generic(char *arg, char *options, int verbose)
>
> static int exportfs_ipv6(char *arg, char *options, int verbose)
> {
> - char *path, *c, hname[NI_MAXHOST + strlen("/128")];
> + char *path, *c;
>
> arg++;
> c = strchr(arg, ']');
> if (c == NULL)
> return 1;
> - strncpy(hname, arg, c - arg);
>
> /* no colon means this is a wildcarded DNS hostname */
> - if (strchr(hname, ':') == NULL)
> + if (memchr(arg, ':', c - arg) == NULL)
> return exportfs_generic(--arg, options, verbose);
>
> path = strstr(c, ":/");
> @@ -370,9 +369,9 @@ static int exportfs_ipv6(char *arg, char *options, int verbose)
>
> /* if there's anything between the closing brace and the
> * path separator, it's probably a prefix length */
> - strcat(hname, ++c);
> + memmove(c, c + 1, path - c);
>
> - exportfs_parsed(hname, path, options, verbose);
> + exportfs_parsed(arg, path, options, verbose);
> return 0;
> }
>
> @@ -458,16 +457,15 @@ static int unexportfs_generic(char *arg, int verbose)
>
> static int unexportfs_ipv6(char *arg, int verbose)
> {
> - char *path, *c, hname[NI_MAXHOST + strlen("/128")];
> + char *path, *c;
>
> arg++;
> c = strchr(arg, ']');
> if (c == NULL)
> return 1;
> - strncpy(hname, arg, c - arg);
>
> /* no colon means this is a wildcarded DNS hostname */
> - if (strchr(hname, ':') == NULL)
> + if (memchr(arg, ':', c - arg) == NULL)
> return unexportfs_generic(--arg, verbose);
>
> path = strstr(c, ":/");
> @@ -477,9 +475,9 @@ static int unexportfs_ipv6(char *arg, int verbose)
>
> /* if there's anything between the closing brace and the
> * path separator, it's probably a prefix length */
> - strcat(hname, ++c);
> + memmove(c, c + 1, path - c);
>
> - unexportfs_parsed(hname, path, verbose);
> + unexportfs_parsed(arg, path, verbose);
> return 0;
> }
>
> --
> 1.8.3.1
>
> --
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--
Chuck Lever
[email protected]