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Check maxlen on strnlen_user usage

PATCH In review Ryan Mallon 2 participants 3 messages Sep 7, 2011 – Sep 8, 2011

Subsystems (2)
VFS exec and binfmt
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Ryan Mallon

author
#0 lore raw

PATCH 1/1 Check maxlen on strnlen_user usage

strnlen_user returns the length of the string including the nul terminator. In the case where maxlen is reached strnlen_user returns maxlen + 1. Most callsites already check for this condition. Fix the call to strnlen_user in fs/exec.c to check for the maxlen case.

Signed-off-by Ryan Mallon <[email protected]>

---

fs/exec.c +1 -1
index 25dcbe5..e19588c 100644
@@ -481,7 +481,7 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
 			goto out;
 
 		len = strnlen_user(str, MAX_ARG_STRLEN);
-		if (!len)
+		if (!len || len>  MAX_ARG_STRLEN)
 			goto out;
 
 		ret = -E2BIG;
#1 lore raw
Quoted 18 lines · On Thu, 08 Sep 2011 09:54:18 +1000 Ryan Mallon <[email protected]> wrote:

strnlen_user returns the length of the string including the nul terminator. In the case where maxlen is reached strnlen_user returns maxlen + 1. Most callsites already check for this condition. Fix the call to strnlen_user in fs/exec.c to check for the maxlen case.

fs/exec.c +1 -1
index 25dcbe5..e19588c 100644
@@ -481,7 +481,7 @@ static int copy_strings(int argc, struct 
 user_arg_ptr argv,
  			goto out;
 
  		len = strnlen_user(str, MAX_ARG_STRLEN);
-		if (!len)
+		if (!len || len>  MAX_ARG_STRLEN)
  			goto out;
Quoted 1 line
  		ret = -E2BIG;

The following call to vald_arg_len() already does this?

This change will cause copy_strings() to incorrectly return -EFAULT, rather than -E2BIG.

Your email client is wordwrapping and space-stuffing the patches, btw.

author
#2 lore raw
Quoted 21 lines · Andrew Morton
Quoted 18 lines · On Thu, 08 Sep 2011 09:54:18 +1000 Ryan Mallon<[email protected]> wrote:

strnlen_user returns the length of the string including the nul terminator. In the case where maxlen is reached strnlen_user returns maxlen + 1. Most callsites already check for this condition. Fix the call to strnlen_user in fs/exec.c to check for the maxlen case.

fs/exec.c +1 -1
index 25dcbe5..e19588c 100644
@@ -481,7 +481,7 @@ static int copy_strings(int argc, struct
 user_arg_ptr argv,
   			goto out;
 
   		len = strnlen_user(str, MAX_ARG_STRLEN);
-		if (!len)
+		if (!len || len>   MAX_ARG_STRLEN)
   			goto out;
Quoted 5 lines
Quoted 1 line
   		ret = -E2BIG;

The following call to vald_arg_len() already does this?

This change will cause copy_strings() to incorrectly return -EFAULT, rather than -E2BIG.

Hmm, missed that. How about the patch below instead which passes the correct length to strnlen_user?

Quoted 1 line

Your email client is wordwrapping and space-stuffing the patches, btw.

I'll try again. Hopefully it works this time.

---
Replace valid_arg_len function in fs/exec.c with max_arg_len function and pass the correct length to strnlen_user.

Signed-off-by Ryan Mallon <[email protected]>

---

fs/exec.c +8 -7
index e19588c..12d2f7f 100644
@@ -296,9 +296,9 @@ err:
 	return err;
 }
 
-static bool valid_arg_len(struct linux_binprm *bprm, long len)
+static long max_arg_len(struct linux_binprm *bprm)
 {
-	return len<= MAX_ARG_STRLEN;
+	return MAX_ARG_STRLEN;
 }
 
 #else

@@ -354,9 +354,9 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
 	return 0;
 }
 
-static bool valid_arg_len(struct linux_binprm *bprm, long len)
+static long max_arg_len(struct linux_binprm *bprm)
 {
-	return len<= bprm->p;
+	return bprm->p;
 }
 
 #endif /* CONFIG_MMU */

@@ -474,18 +474,19 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
 		const char __user *str;
 		int len;
 		unsigned long pos;
+		long max_len = max_arg_len(bprm);
 
 		ret = -EFAULT;
 		str = get_user_arg_ptr(argv, argc);
 		if (IS_ERR(str))
 			goto out;
 
-		len = strnlen_user(str, MAX_ARG_STRLEN);
-		if (!len || len>  MAX_ARG_STRLEN)
+		len = strnlen_user(str, max_len);
+		if (!len)
 			goto out;
 
 		ret = -E2BIG;
-		if (!valid_arg_len(bprm, len))
+		if (len>  max_len)
 			goto out;
 
 		/* We're going to work our way backwords. */