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SubjectRe: [PATCH v1] seq_file: Fix overflow condition in seq_commit
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On Tue, Aug 20, 2013 at 7:04 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Tue, Aug 20, 2013 at 08:36:22AM +0100, Al Viro wrote:
>
>> Aha. _That_ is a bug, all right - dynamic_dname() is simply not suitable
>> for that kind of uses. ashmem.c is certainly abusing shmem_file_setup();
>> feeding that kind of mess as dentry name is a Bad Idea(tm). Anyway,
>> I'd suggest this for a fix:
>>
>> va_list args;
>> size_t sz;
>> va_start(args, fmt);
>> sz = vsnprintf(NULL, 0, fmt, args) + 1;
>> va_end(args);
>> if (sz > buflen)
>> return ERR_PTR(-ENAMETOOLONG);
>> va_start(args, fmt);
>> buffer += buflen - sz;
>> vsprintf(buffer, fmt, args);
>> va_end(args);
>> return buffer;
>>
>> Either right in dynamic_dname(), or as possibly_fucking_long_dname(),
>> to be used by shmem.c...
>
> Actually, looking at the users of dynamic_dname()... Most of them are
> fine with dynamic_dname() as it is, with 2 possible exceptions:
> hugetlb_dname() and shmem_dname(). Both are using "/%s (deleted)",
> dentry->d_name.name as format... So the solution above may very
> well be an overkill; something like
>
> char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
> {
> char *end = buffer + buflen;
> /* these dentries are never renamed, so d_lock is not needed */
> if (prepend(&end, &buflen, " (deleted)", 11) ||
> prepend_name(&end, &buflen, &dentry->d_name) ||
> prepend(&end, &buflen, "/", 1))
> end = ERR_PTR(-ENAMETOOLONG);
> return end;
> }
>
> will do for those two. Care to test the diff below?
>
> cope with potentially long ->d_dname() output for shmem/hugetlb
>
> dynamic_dname() is both too much and too little for those - the
> output may be well in excess of 64 bytes dynamic_dname() assumes
> to be enough (thanks to ashmem feeding really long names to
> shmem_file_setup()) and vsnprintf() is an overkill for those
> guys.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 87bdb53..83cfb83 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2724,6 +2724,17 @@ char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
> return memcpy(buffer, temp, sz);
> }
>
> +char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
> +{
> + char *end = buffer + buflen;
> + /* these dentries are never renamed, so d_lock is not needed */
> + if (prepend(&end, &buflen, " (deleted)", 11) ||
> + prepend_name(&end, &buflen, &dentry->d_name) ||
> + prepend(&end, &buflen, "/", 1))
> + end = ERR_PTR(-ENAMETOOLONG);
> + return end;
> +}
> +
> /*
> * Write full pathname from the root of the filesystem into the buffer.
> */
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index a3f868a..4e5f332 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -916,14 +916,8 @@ static int get_hstate_idx(int page_size_log)
> return h - hstates;
> }
>
> -static char *hugetlb_dname(struct dentry *dentry, char *buffer, int buflen)
> -{
> - return dynamic_dname(dentry, buffer, buflen, "/%s (deleted)",
> - dentry->d_name.name);
> -}
> -
> static struct dentry_operations anon_ops = {
> - .d_dname = hugetlb_dname
> + .d_dname = simple_dname
> };
>
> /*
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index b90337c..4a12532 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -336,6 +336,7 @@ extern int d_validate(struct dentry *, struct dentry *);
> * helper function for dentry_operations.d_dname() members
> */
> extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
> +extern char *simple_dname(struct dentry *, char *, int);
>
> extern char *__d_path(const struct path *, const struct path *, char *, int);
> extern char *d_absolute_path(const struct path *, char *, int);
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 8335dbd..e43dc55 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2909,14 +2909,8 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
>
> /* common code */
>
> -static char *shmem_dname(struct dentry *dentry, char *buffer, int buflen)
> -{
> - return dynamic_dname(dentry, buffer, buflen, "/%s (deleted)",
> - dentry->d_name.name);
> -}
> -
> static struct dentry_operations anon_ops = {
> - .d_dname = shmem_dname
> + .d_dname = simple_dname
> };
>
> /**
> --
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Can this patch (committed as 118b23022512eb2f41ce42db70dc0568d00be4ba
upstream) go in stable? It fixes a regression introduced in 3.9
dumping /proc/pid/maps for processes with ashmem regions with long
names.


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