Live › vulnerability › CVE-2026-98803
Go to dashboardIn the Linux kernel's stmmac Ethernet driver, frames larger than the RX buffer were written into an unmapped secondary buffer, causing IOMMU translation faults. The kernel fix enables proper scatter-gather RX buffer allocation on GMAC4 and XGMAC cores.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Systems running the Linux kernel with the stmmac Ethernet driver on GMAC4 or XGMAC cores, especially IOMMU-based ARM platforms, where oversized frames can overflow the first RX buffer. Systems without stmmac hardware or without an IOMMU are less likely to show the reported fault, though the sources do not state this explicitly. AF_XDP zero-copy RX remains exposed per the description.
No product ranges from the sources yet.
lsmod | grep stmmac or dmesg | grep stmmac (unknown whether the sources name a specific command)dmesg (unknown whether the sources list a specific string beyond the sample log)Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
net: stmmac: fix rx Scatter-Gather support
When a received frame is larger than dma_buf_sz, the DMA scatters it across multiple RX descriptors (rx Scatter-Gather). The secondary RX buffer (sec_page) was only allocated and programmed when split-header (SPH) was active, so for regular frames buffer2 was neither allocated nor backed by a valid mapping. As soon as an incoming frame overflowed buffer1, the DMA wrote the overflow into the unmapped secondary-buffer address, triggering an SMMU translation fault on IOMMU-based platforms:
arm-smmu 15000000.iommu: Unhandled context fault: fsr=0x402, iova=0x00000000, fsynr=0x7f0011, cbfrsynra=0x1c90, cb=11 arm-smmu 15000000.iommu: FSR = 00000402 [Format=2 TF], SID=0x1c90 arm-smmu 15000000.iommu: FSYNR0 = 007f0011 [S1CBNDX=127 WNR PLVL=1]
Enable scatter-gather for non-SPH frames on cores that can program an independent secondary RX buffer (GMAC4/XGMAC): allocate and mark buffer2 as valid in stmmac_init_rx_buffers() and stmmac_rx_refill(), and account for it in the buffer length computation. Legacy cores have no set_sec_addr op, so they keep buffer2 disabled.
Since buffer2 is handed to the DMA at page offset 0, the page pool sync window is widened to cover both buffers in every mode: offset is set to 0 and max_len to dma_buf_sz + stmmac_rx_offset().
The FCS can straddle the buffer1/buffer2 boundary and a descriptor boundary, so it is now stripped from the tail of the assembled frame with pskb_trim() instead of from a single buffer, avoiding an unsigned underflow for frames that overflow a buffer by 1..3 bytes. For single-buffer frames the XDP program must not see the FCS, so it is removed from the XDP buffer before the program runs.
Native XDP currently only supports single-buffer (linear) frames. An oversized frame accepted by the MAC (jumbo enabled) is received via buffer2; the XDP program only sees buffer1, so on a TX/REDIRECT verdict the frame is forwarded truncated. XDP multi-buffer support to handle this case is planned as a follow-up.
AF_XDP zero-copy RX is not covered by this change: a ZC queue still programs buffer2 at DMA address 0 (and XGMAC has no buffer2-valid bit), so an oversized frame overflowing buffer1 can still trigger the same SMMU translation fault. Handling is planned as a follow-up.
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