[v3 PATCH 3/3] mm/mempolicy: unify the parameter sanity check for mbind and set_mempolicy

From: Feng Tang
Date: Mon May 31 2021 - 11:17:03 EST


Currently the kernel_mbind() and kernel_set_mempolicy() do almost
the same operation for parameter sanity check.

Add a helper function to unify the code to reduce the redundancy,
and make it easier for changing the pre-processing code in future.

[thanks to David Rientjes for suggesting using helper function
instead of macro]

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
mm/mempolicy.c | 47 +++++++++++++++++++++++++++++------------------
1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c337bd7..85ef512 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1444,26 +1444,37 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
}

+static inline int sanitize_mpol_flags(int *mode, unsigned short *flags)
+{
+ *flags = *mode & MPOL_MODE_FLAGS;
+ *mode &= ~MPOL_MODE_FLAGS;
+ if ((unsigned int)(*mode) >= MPOL_MAX)
+ return -EINVAL;
+ if ((*flags & MPOL_F_STATIC_NODES) && (*flags & MPOL_F_RELATIVE_NODES))
+ return -EINVAL;
+
+ return 0;
+}
+
static long kernel_mbind(unsigned long start, unsigned long len,
unsigned long mode, const unsigned long __user *nmask,
unsigned long maxnode, unsigned int flags)
{
+ unsigned short mode_flags;
nodemask_t nodes;
+ int lmode = mode;
int err;
- unsigned short mode_flags;

start = untagged_addr(start);
- mode_flags = mode & MPOL_MODE_FLAGS;
- mode &= ~MPOL_MODE_FLAGS;
- if (mode >= MPOL_MAX)
- return -EINVAL;
- if ((mode_flags & MPOL_F_STATIC_NODES) &&
- (mode_flags & MPOL_F_RELATIVE_NODES))
- return -EINVAL;
+ err = sanitize_mpol_flags(&lmode, &mode_flags);
+ if (err)
+ return err;
+
err = get_nodes(&nodes, nmask, maxnode);
if (err)
return err;
- return do_mbind(start, len, mode, mode_flags, &nodes, flags);
+
+ return do_mbind(start, len, lmode, mode_flags, &nodes, flags);
}

SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
@@ -1477,20 +1488,20 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
unsigned long maxnode)
{
- int err;
+ unsigned short mode_flags;
nodemask_t nodes;
- unsigned short flags;
+ int lmode = mode;
+ int err;
+
+ err = sanitize_mpol_flags(&lmode, &mode_flags);
+ if (err)
+ return err;

- flags = mode & MPOL_MODE_FLAGS;
- mode &= ~MPOL_MODE_FLAGS;
- if ((unsigned int)mode >= MPOL_MAX)
- return -EINVAL;
- if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
- return -EINVAL;
err = get_nodes(&nodes, nmask, maxnode);
if (err)
return err;
- return do_set_mempolicy(mode, flags, &nodes);
+
+ return do_set_mempolicy(lmode, mode_flags, &nodes);
}

SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
--
2.7.4