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device-nodes: always NUL-terminate encode_devnode_name() output - #44424
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Reviewed 9004056 (architecture, correctness, lifetimes, security, style, tests). No new issues found, 2 still open. Suggestions
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| memset(buf, 'X', sizeof(buf)); | ||
| ASSERT_OK(encode_devnode_name("abcdefg", buf, sizeof(buf))); | ||
| ASSERT_STREQ(buf, "abcdefg"); |
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Claude: suggestion: No success case ends with a multi-byte sequence exactly at the buffer end, so the < → <= seqlen check isn't pinned down; an over-strict off-by-one would still pass. Add e.g. ASSERT_OK(encode_devnode_name("ab一", buf, 6)); ASSERT_STREQ(buf, "ab一");.
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Added as a success case with len 6.
| char buf[8]; | ||
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| /* On truncation the output must still be NUL terminated, and only contain complete sequences */ | ||
| memset(buf, 'X', sizeof(buf)); |
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Claude: nit: The new len == 0 guard is untested, yet it is what keeps the truncated: path from writing str_enc[0] into a zero-sized buffer. Add a len = 0 case (EINVAL, buffer untouched) and a len = 1 case (EINVAL, empty string).
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Added both the len 0 and len 1 cases.
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Please do not stack fix, but squash. |
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Squashed into a single commit, content unchanged. |
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Please also address suggestions by Claude. |
When the encoded string does not fit, encode_devnode_name() returned -EINVAL without terminating the output buffer. The callers in usb_id, ata_id and scsi_id ignore the return value and add the buffer as a property. With a USB product or manufacturer string that fills the 256-byte buffer in usb_id exactly (e.g. 85 three-byte UTF-8 characters followed by one ASCII letter) udevd then reads past the end of the stack array and copies adjacent stack bytes into ID_MODEL_ENC/ID_VENDOR_ENC. Leave room for the NUL in each length check and terminate the truncated output on failure. Output for strings that fit is unchanged.
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Added both: a success case with a multi-byte sequence ending right before the NUL ("ab一" into 6 bytes), and the len 0 / len 1 cases (EINVAL with the buffer untouched, EINVAL with an empty string). Squashed into the single commit, no change to the fix itself. |
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Repro: a USB device whose product string is 85 x U+4E00 followed by one ASCII letter fills the 256-byte model_str_enc buffer in usb_id exactly, and udevd then strdup()s ID_MODEL_ENC past the end of the stack array. A standalone ASan harness reports a 257-byte read from a 256-byte buffer, and the new test case fails on the current code.
Cause: encode_devnode_name() returns -EINVAL without writing the terminating NUL when the output does not fit, while usb_id, ata_id and scsi_id ignore the return value and export the buffer as a property. Adjacent stack bytes end up in ID_MODEL_ENC/ID_USB_MODEL_ENC, which unprivileged users can read with udevadm info.
Fix: reserve room for the NUL in every length check and terminate the truncated output on failure, so all callers get a valid string without each one having to handle the error. Output for strings that fit is unchanged.