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[2/2] libdecnumber: fixed undefined behavior in decNumberGetBCD.

Message ID 20240202150948.42888-1-icmccorm@andrew.cmu.edu
State Accepted
Headers
Series [1/2] libdecnumber: fixed undefined behavior in `decFloatFMA` |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Ian McCormack Feb. 2, 2024, 3:09 p.m. UTC 
  This patch fixes a minor instance of undefined behavior in libdecnumber. It was discovered in the Rust bindings for libdecnumber (`dec`) using a custom version of MIRI that can execute foreign functions.

On the last iteration of the `while` loop in `decNumberGetBCD`, the pointer `up` will be incremented beyond the end of the allocation `dn->lsu` before the assignment `u=*up`. This value does not affect the termination of the loop and is never read again, so this isn't really an issue, but this patch prevent an access out-of-bounds by only incrementing `up` if it is safe to do so.

Bootstrapped on x86_64-pc-linux-gnu with no regressions.

libdecnumber/ChangeLog
       * decNumber.c: In `decNumberGetBCD`, only read from `dn->lsu` while the pointer `up` is still within bounds.

---
 libdecnumber/decNumber.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
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Patch

diff --git a/libdecnumber/decNumber.c b/libdecnumber/decNumber.c
index 0b6eb160fe3..094bc51c14a 100644
--- a/libdecnumber/decNumber.c
+++ b/libdecnumber/decNumber.c
@@ -3463,7 +3463,8 @@  uByte * decNumberGetBCD(const decNumber *dn, uByte *bcd) {
       cut--;
       if (cut>0) continue;	   /* more in this unit */
       up++;
-      u=*up;
+      if (ub > bcd)
+        u=*up;
       cut=DECDPUN;
       }
   #endif