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SubjectIs it OK to export symbols 'getname' and 'putname'?
Hi Al,

On Sun, Apr 12, 2015 at 02:13:18AM +0100, Al Viro wrote:
>
> BTW, looking at the __getname() callers... Lustre one sure as hell looks
> bogus:
> char *tmp = __getname();
>
> if (!tmp)
> return ERR_PTR(-ENOMEM);
>
> len = strncpy_from_user(tmp, filename, PATH_MAX);
> if (len == 0)
> ret = -ENOENT;
> else if (len > PATH_MAX)
> ret = -ENAMETOOLONG;
>
> if (ret) {
> __putname(tmp);
> tmp = ERR_PTR(ret);
> }
> return tmp;
>
> Note that
> * strncpy_from_user(p, u, n) can return a negative (-EFAULT)
> * strncpy_from_user(p, u, n) cannot return a positive greater than
> n. In case of missing NUL among the n bytes starting at u (and no faults
> accessing those) we get exactly n bytes copied and n returned. In case
> when NUL is there, we copy everything up to and including that NUL and
> return number of non-NUL bytes copied.
>
> IOW, these failure cases had never been tested. Name being too long ends up
> with non-NUL-terminated array of characters returned, and the very first
> caller of ll_getname() feeds it to strlen(). Fault ends up with uninitialized
> array...
>
> AFAICS, the damn thing should just use getname() and quit reinventing the
> wheel, badly.
>

I'm trying to clean that part of code you mentioned, and I found I have
to export the symbols 'getname' and 'putname' as follow to replace that
__getname() caller:

diff --git a/drivers/staging/lustre/lustre/llite/dir.c b/drivers/staging/lustre/lustre/llite/dir.c
index a182019..014f51a 100644
--- a/drivers/staging/lustre/lustre/llite/dir.c
+++ b/drivers/staging/lustre/lustre/llite/dir.c
@@ -1216,29 +1216,8 @@ out:
return rc;
}

-static char *
-ll_getname(const char __user *filename)
-{
- int ret = 0, len;
- char *tmp = __getname();
-
- if (!tmp)
- return ERR_PTR(-ENOMEM);
-
- len = strncpy_from_user(tmp, filename, PATH_MAX);
- if (len == 0)
- ret = -ENOENT;
- else if (len > PATH_MAX)
- ret = -ENAMETOOLONG;
-
- if (ret) {
- __putname(tmp);
- tmp = ERR_PTR(ret);
- }
- return tmp;
-}
-
-#define ll_putname(filename) __putname(filename)
+#define ll_getname(filename) getname(filename)
+#define ll_putname(name) putname(name)

static long ll_dir_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
@@ -1441,6 +1420,7 @@ free_lmv:
return rc;
}
case LL_IOC_REMOVE_ENTRY: {
+ struct filename *name = NULL;
char *filename = NULL;
int namelen = 0;
int rc;
@@ -1453,20 +1433,17 @@ free_lmv:
if (!(exp_connect_flags(sbi->ll_md_exp) & OBD_CONNECT_LVB_TYPE))
return -ENOTSUPP;

- filename = ll_getname((const char *)arg);
- if (IS_ERR(filename))
- return PTR_ERR(filename);
+ name = ll_getname((const char *)arg);
+ if (IS_ERR(name))
+ return PTR_ERR(name);

+ filename = name->name;
namelen = strlen(filename);
- if (namelen < 1) {
- rc = -EINVAL;
- goto out_rmdir;
- }

rc = ll_rmdir_entry(inode, filename, namelen);
out_rmdir:
- if (filename)
- ll_putname(filename);
+ if (name)
+ ll_putname(name);
return rc;
}
case LL_IOC_LOV_SWAP_LAYOUTS:
@@ -1481,15 +1458,17 @@ out_rmdir:
struct lov_user_md *lump;
struct lov_mds_md *lmm = NULL;
struct mdt_body *body;
+ struct filename *name;
char *filename = NULL;
int lmmsize;

if (cmd == IOC_MDC_GETFILEINFO ||
cmd == IOC_MDC_GETFILESTRIPE) {
- filename = ll_getname((const char *)arg);
- if (IS_ERR(filename))
- return PTR_ERR(filename);
+ name = ll_getname((const char *)arg);
+ if (IS_ERR(name))
+ return PTR_ERR(name);

+ filename = name->name;
rc = ll_lov_getstripe_ea_info(inode, filename, &lmm,
&lmmsize, &request);
} else {
diff --git a/fs/namei.c b/fs/namei.c
index ffab2e0..7a0948c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -205,6 +205,7 @@ getname(const char __user * filename)
{
return getname_flags(filename, 0, NULL);
}
+EXPORT_SYMBOL(getname);

struct filename *
getname_kernel(const char * filename)
@@ -254,6 +255,7 @@ void putname(struct filename *name)
} else
__putname(name);
}
+EXPORT_SYMBOL(putname);

static int check_acl(struct inode *inode, int mask)
{


Is that a good idea to export these symbols, given that lustre may be
the only user?

Looking forward to your insight.

Thanks,
Boqun
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