Handle bogus %cs selector in single-step instruction decoding (CVE-2007-3731)

The code for LDT segment selectors was not robust in the face of a bogus
selector set in %cs via ptrace before the single-step was done.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 5c1fb6aada5bfe3975fe103de3292e329eebf980..de779c03df9e887b38e3a8f65728608d0fa21033 100644 (file)
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -172,14 +172,22 @@ static unsigned long convert_eip_to_linear(struct task_struct *child, struct pt_
                u32 *desc;
                unsigned long base;
 
-               down(&child->mm->context.sem);
-               desc = child->mm->context.ldt + (seg & ~7);
-               base = (desc[0] >> 16) | ((desc[1] & 0xff) << 16) | (desc[1] & 0xff000000);
+               seg &= ~7UL;
 
-               /* 16-bit code segment? */
-               if (!((desc[1] >> 22) & 1))
-                       addr &= 0xffff;
-               addr += base;
+               down(&child->mm->context.sem);
+               if (unlikely((seg >> 3) >= child->mm->context.size))
+                       addr = -1L; /* bogus selector, access would fault */
+               else {
+                       desc = child->mm->context.ldt + seg;
+                       base = ((desc[0] >> 16) |
+                               ((desc[1] & 0xff) << 16) |
+                               (desc[1] & 0xff000000));
+
+                       /* 16-bit code segment? */
+                       if (!((desc[1] >> 22) & 1))
+                               addr &= 0xffff;
+                       addr += base;
+               }
                up(&child->mm->context.sem);
        }
        return addr;

diff --git a/arch/x86_64/kernel/ptrace.c b/arch/x86_64/kernel/ptrace.c
index a2422ecb8dfa74001fd103fa48470b8bf71a7707..70840577383d4b86d6e1eba65a63c862b564938d 100644 (file)
--- a/arch/x86_64/kernel/ptrace.c
+++ b/arch/x86_64/kernel/ptrace.c
@@ -103,16 +103,25 @@ unsigned long convert_rip_to_linear(struct task_struct *child, struct pt_regs *r
                u32 *desc;
                unsigned long base;
 
-               down(&child->mm->context.sem);
-               desc = child->mm->context.ldt + (seg & ~7);
-               base = (desc[0] >> 16) | ((desc[1] & 0xff) << 16) | (desc[1] & 0xff000000);
+               seg &= ~7UL;
 
-               /* 16-bit code segment? */
-               if (!((desc[1] >> 22) & 1))
-                       addr &= 0xffff;
-               addr += base;
+               down(&child->mm->context.sem);
+               if (unlikely((seg >> 3) >= child->mm->context.size))
+                       addr = -1L; /* bogus selector, access would fault */
+               else {
+                       desc = child->mm->context.ldt + seg;
+                       base = ((desc[0] >> 16) |
+                               ((desc[1] & 0xff) << 16) |
+                               (desc[1] & 0xff000000));
+
+                       /* 16-bit code segment? */
+                       if (!((desc[1] >> 22) & 1))
+                               addr &= 0xffff;
+                       addr += base;
+               }
                up(&child->mm->context.sem);
        }
+
        return addr;
 }