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@xxxxxxxxxxxxxxxxxx>
---
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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