| Message ID | 20241027193541.14212-1-mottikumarbabu@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Fix out-of-bounds access in xfs_bmapi_allocate by validating whichfork | expand |
Hi everyone, I hope this message finds you well. I wanted to follow up on my previously submitted patch titled "[PATCH] Fix out-of-bounds access in xfs_bmapi_allocate by validating whichfork." As a reminder, this patch addresses an issue reported by Coverity Scan (CID 1633175), where the variable `whichfork` can take invalid values, specifically `2`, leading to an out-of-bounds access in `xfs_bmbt_init_cursor`. The added validation check ensures that `whichfork` remains within the valid range of 0 or 1. If it falls outside this range, the function will return `-EINVAL`, enhancing the code's robustness and preventing potential crashes or undefined behavior. I appreciate any feedback or suggestions you might have. Best, MottiKumar Babu mottikumarbabu@gmail.com
On Mon, Oct 28, 2024 at 01:05:27AM +0530, MottiKumar Babu wrote: > This issue was reported by Coverity Scan. > > Report: > CID 1633175 Out-of-bounds access - Access of memory not owned by this buffer may cause crashes or incorrect computations. > In xfs_bmapi_allocate: Out-of-bounds access to a buffer (CWE-119) We really need more details than thisi about the issue. I have no idea what issue this describes, nor the code which it refers to. Where is the out of bounds memory access occurring, how does it trigger and where does the code end up crashing as a result? A link to the coverity report woudl certainly help.... > Signed-off-by: MottiKumar Babu <mottikumarbabu@gmail.com> > --- > fs/xfs/libxfs/xfs_bmap.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c > index 36dd08d13293..6ff378d2d3d9 100644 > --- a/fs/xfs/libxfs/xfs_bmap.c > +++ b/fs/xfs/libxfs/xfs_bmap.c > @@ -4169,6 +4169,10 @@ xfs_bmapi_allocate( > * is not on the busy list. > */ > bma->datatype = XFS_ALLOC_NOBUSY; > + // Ensure whichfork is valid (0 or 1) before further checks > + if (whichfork < 0 || whichfork > 1) { > + return -EINVAL; // Invalid fork > + } > if (whichfork == XFS_DATA_FORK || whichfork == XFS_COW_FORK) { > bma->datatype |= XFS_ALLOC_USERDATA; > if (bma->offset == 0) That's not going to work. If you look at how whichfork is initialised early on in the xfs_bmapi_allocate() function, you'll see it calls this function: static inline int xfs_bmapi_whichfork(uint32_t bmapi_flags) { if (bmapi_flags & XFS_BMAPI_COWFORK) return XFS_COW_FORK; else if (bmapi_flags & XFS_BMAPI_ATTRFORK) return XFS_ATTR_FORK; return XFS_DATA_FORK; } A value of 2 (XFS_COW_FORK) is definitely a valid value for whichfork to have. Indeed, the line of code after the fix checks if whichfork == XFS_COW_FORK, indicating that such a value is expected and should be handled correctly. However, this patch will result in rejecting any request to allocate blocks in the XFS_COW_FORK. This will fail any COW operation we try to perform with -EINVAL. i.e. overwrites after a reflink copy will fail. This sort of regression would be picked up very quickly by fstests. Hence it is important that any change - even simple changes - are regression tested before they are proposed for review and merge.... -Dave.
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index 36dd08d13293..6ff378d2d3d9 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -4169,6 +4169,10 @@ xfs_bmapi_allocate( * is not on the busy list. */ bma->datatype = XFS_ALLOC_NOBUSY; + // Ensure whichfork is valid (0 or 1) before further checks + if (whichfork < 0 || whichfork > 1) { + return -EINVAL; // Invalid fork + } if (whichfork == XFS_DATA_FORK || whichfork == XFS_COW_FORK) { bma->datatype |= XFS_ALLOC_USERDATA; if (bma->offset == 0)
This issue was reported by Coverity Scan. Report: CID 1633175 Out-of-bounds access - Access of memory not owned by this buffer may cause crashes or incorrect computations. In xfs_bmapi_allocate: Out-of-bounds access to a buffer (CWE-119) Signed-off-by: MottiKumar Babu <mottikumarbabu@gmail.com> --- fs/xfs/libxfs/xfs_bmap.c | 4 ++++ 1 file changed, 4 insertions(+)