Re: [patch v2] sunrpc: integer underflow in rsc_parse()

On Tue, Feb 24, 2015 at 10:54:44PM -0500, Simo Sorce wrote:

On Tue, 2015-02-24 at 18:34 +0300, Dan Carpenter wrote:

quoted

If we call groups_alloc() with invalid values then it's might lead to
memory corruption.  For example, with a negative value then we might not
allocate enough for sizeof(struct group_info).

Signed-off-by: Dan Carpenter <redacted>
---
v2:  In v1, I changed groups_alloc().  The other places which call
groups_alloc() check the value before calling.  Eric wanted that, either
have all the callers check, or all the callers rely on groups_alloc().
In the end, Bruce Fields said adding the check here was probably
reasonable.

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index 224a82f..1095be9 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c

@@ -463,6 +463,8 @@ static int rsc_parse(struct cache_detail *cd,
 		/* number of additional gid's */
 		if (get_int(&mesg, &N))
 			goto out;
+		if (N < 0 || N > NGROUPS_MAX)
+			goto out;
 		status = -ENOMEM;
 		rsci.cred.cr_group_info = groups_alloc(N);
 		if (rsci.cred.cr_group_info == NULL)
--

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I touched this code relatively recently, and this check looks correct.
Feel free to add Reviewed-by: Simo Sorce [off-list ref]

Thanks!  I thought your below-the-line context was useful, so pulled a
version of it into the commit.

--b.

commit 76cb4be993c0
Author: Dan Carpenter [off-list ref]
Date:   Tue Feb 24 18:34:01 2015 +0300

    sunrpc: integer underflow in rsc_parse()
    
    If we call groups_alloc() with invalid values then it's might lead to
    memory corruption.  For example, with a negative value then we might not
    allocate enough for sizeof(struct group_info).
    
    (We're doing this in the caller for consistency with other callers of
    groups_alloc().  The other alternative might be to move the check out of
    all the callers into groups_alloc().)
    
    Signed-off-by: Dan Carpenter [off-list ref]
    Reviewed-by: Simo Sorce [off-list ref]
    Signed-off-by: J. Bruce Fields [off-list ref]

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index 224a82f24d3c..1095be9c80ab 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c

@@ -463,6 +463,8 @@ static int rsc_parse(struct cache_detail *cd,
 		/* number of additional gid's */
 		if (get_int(&mesg, &N))
 			goto out;
+		if (N < 0 || N > NGROUPS_MAX)
+			goto out;
 		status = -ENOMEM;
 		rsci.cred.cr_group_info = groups_alloc(N);
 		if (rsci.cred.cr_group_info == NULL)