{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63895","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-07-19T07:54:57.019Z","datePublished":"2026-07-19T14:55:05.479Z","dateUpdated":"2026-07-19T14:55:05.479Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-07-19T14:55:05.479Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: copy only received bytes on short ep0 read\n\nffs_ep0_read() allocates its control-OUT data buffer with\nkmalloc() (not kzalloc) at the Length value from the Setup\npacket, then copies that full len to userspace regardless of\nhow many bytes were actually received:\n\n    data = kmalloc(len, GFP_KERNEL);\n    ...\n    ret = __ffs_ep0_queue_wait(ffs, data, len);\n    if ((ret > 0) && (copy_to_user(buf, data, len)))\n            ret = -EFAULT;\n\n__ffs_ep0_queue_wait() returns req->actual, which on a short\ncontrol OUT transfer is strictly less than len.  The\ncopy_to_user() call still copies len bytes, so on a short OUT\nthe last (len - ret) bytes of the kmalloc() buffer --\nuninitialised slab residue -- are delivered to the FunctionFS\ndaemon.\n\nShort ep0 OUT completions are specified USB control-transfer\nbehavior and are produced by in-tree UDCs:\n\n  * dwc2 continues on req->actual < req->length for ep0 DATA OUT\n    (short-not-ok is the only ep0-OUT stall path).\n  * aspeed_udc ends ep0 OUT on rx_len < ep->ep.maxpacket.\n  * renesas_usbf logs \"ep0 short packet\" and completes the\n    request.\n  * dwc3 stalls on short IN but not on short OUT.\n\nA short ep0 OUT is therefore not evidence of a broken UDC; it is\na normal condition f_fs has to cope with.  The sibling gadgetfs\nimplementation in drivers/usb/gadget/legacy/inode.c already does\nthis correctly via min(len, dev->req->actual) before\ncopy_to_user().  This patch brings f_fs.c to the same safe\npattern rather than trimming at a defensive layer.\n\nThe bug is reached from the FunctionFS device node, which in\nreal deployments is owned by the privileged gadget daemon\n(adbd, UMS, composite gadget services, etc.); it is not\nreachable from unprivileged userspace.  Linux host stacks\nnormally reject short-wLength control OUTs before they reach\nthe gadget, so reproducing this required a build that\nbypasses that host-side check.  With the bypass in place, a\n1-byte payload on a 64-byte Setup produces 63 bytes of\nnon-canary slab residue in the daemon's read buffer.\n\nFix by copying only ret (actually received) bytes to\nuserspace."}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/usb/gadget/function/f_fs.c"],"versions":[{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"90ccf5fb63243fae1b4b3200f3310500500ecf2e","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"af32dbb2ca0b3d09271ab718d13857a457fa16f2","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"e835bf9a055f71874065a40780ca5560b7df8b33","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"88874a19b2b093bfaaa1c0090fa536c44da8c08b","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"607730a414773a7cbe3037a64a6c64e72689ff5e","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"23c1f7deb9dd8447ecde749850676302aa1e2bd3","status":"affected","versionType":"git"},{"version":"ddf8abd2599491cbad959c700b90ba72a5dce8d0","lessThan":"4e036c10e7f4df5d951c69cc3697bc8e209c6d02","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/usb/gadget/function/f_fs.c"],"versions":[{"version":"2.6.35","status":"affected"},{"version":"0","lessThan":"2.6.35","status":"unaffected","versionType":"semver"},{"version":"5.15.210","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"6.1.176","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.143","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.93","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.35","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.0.12","lessThanOrEqual":"7.0.*","status":"unaffected","versionType":"semver"},{"version":"7.1","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"5.15.210"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"6.1.176"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"6.6.143"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"6.12.93"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"6.18.35"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"7.0.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.35","versionEndExcluding":"7.1"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"},{"url":"https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"},{"url":"https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"},{"url":"https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"},{"url":"https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e"},{"url":"https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3"},{"url":"https://git.kernel.org/stable/c/4e036c10e7f4df5d951c69cc3697bc8e209c6d02"}],"title":"usb: gadget: f_fs: copy only received bytes on short ep0 read","x_generator":{"engine":"bippy-1.2.0"}}}}