linux-kernel - Is it OK to export symbols 'getname' and 'putname'?

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Message-ID: <20150417123530.GA4249@fixme-laptop.cn.ibm.com>
Date:	Fri, 17 Apr 2015 20:35:30 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Is 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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