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

Handle bogus %cs selector in single-step instruction decoding

mainline: 29eb51101c02df517ca64ec472d7501127ad1da8

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: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Jeff Mahoney <jeffm@suse.com>
CC: Oliver Pinter <oliver.pntr@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 0c0ceec5de009e025c214b4c0f8af7f9d607510e..120a63be17bf8aaa24b9ae664517c52312f1455b 100644 (file)
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -164,14 +164,22 @@ 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 8d89d8ce4c8fef9023940654d40d6dba9e08cba1..7fc0e737a37e61863e7eed4dd98d13e25594eafb 100644 (file)
--- a/arch/x86_64/kernel/ptrace.c
+++ b/arch/x86_64/kernel/ptrace.c
@@ -102,16 +102,25 @@ 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;
 }