[Xen-devel] [patch] xen: off by one errors in multicalls.c

[Dan Carpenter <error27@xxxxxxxxx>]

b->args[] has MC_ARGS elements, so the comparison here should be
">=" instead of ">".  Otherwise we read past the end of the array
one space.

Signed-off-by: Dan Carpenter <error27@xxxxxxxxx>
---
This is a static checker patch and I haven't tested it.  Please
review carefully.

diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index 8bff7e7..1b2b73f 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -189,10 +189,10 @@ struct multicall_space __xen_mc_entry(size_t args)
        unsigned argidx = roundup(b->argidx, sizeof(u64));
 
        BUG_ON(preemptible());
-       BUG_ON(b->argidx > MC_ARGS);
+       BUG_ON(b->argidx >= MC_ARGS);
 
        if (b->mcidx == MC_BATCH ||
-           (argidx + args) > MC_ARGS) {
+           (argidx + args) >= MC_ARGS) {
                mc_stats_flush(b->mcidx == MC_BATCH ? FL_SLOTS : FL_ARGS);
                xen_mc_flush();
                argidx = roundup(b->argidx, sizeof(u64));
@@ -206,7 +206,7 @@ struct multicall_space __xen_mc_entry(size_t args)
        ret.args = &b->args[argidx];
        b->argidx = argidx + args;
 
-       BUG_ON(b->argidx > MC_ARGS);
+       BUG_ON(b->argidx >= MC_ARGS);
        return ret;
 }
 
@@ -216,7 +216,7 @@ struct multicall_space xen_mc_extend_args(unsigned long op, 
size_t size)
        struct multicall_space ret = { NULL, NULL };
 
        BUG_ON(preemptible());
-       BUG_ON(b->argidx > MC_ARGS);
+       BUG_ON(b->argidx >= MC_ARGS);
 
        if (b->mcidx == 0)
                return ret;
@@ -224,14 +224,14 @@ struct multicall_space xen_mc_extend_args(unsigned long 
op, size_t size)
        if (b->entries[b->mcidx - 1].op != op)
                return ret;
 
-       if ((b->argidx + size) > MC_ARGS)
+       if ((b->argidx + size) >= MC_ARGS)
                return ret;
 
        ret.mc = &b->entries[b->mcidx - 1];
        ret.args = &b->args[b->argidx];
        b->argidx += size;
 
-       BUG_ON(b->argidx > MC_ARGS);
+       BUG_ON(b->argidx >= MC_ARGS);
        return ret;
 }
 

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