Description

In the Linux kernel, the following vulnerability has been resolved: vt: discard stale unicode buffer on alt screen exit after resize When enter_alt_screen() saves vc_uni_lines into vc_saved_uni_lines and sets vc_uni_lines to NULL, a subsequent console resize via vc_do_resize() skips reallocating the unicode buffer because vc_uni_lines is NULL. However, vc_saved_uni_lines still points to the old buffer allocated for the original dimensions. When leave_alt_screen() later restores vc_saved_uni_lines, the buffer dimensions no longer match vc_rows/vc_cols. Any operation that iterates over the unicode buffer using the current dimensions (e.g. csi_J clearing the screen) will access memory out of bounds, causing a kernel oops: BUG: unable to handle page fault for address: 0x0000002000000020 RIP: 0010:csi_J+0x133/0x2d0 The faulting address 0x0000002000000020 is two adjacent u32 space characters (0x20) interpreted as a pointer, read from the row data area past the end of the 25-entry pointer array in a buffer allocated for 80x25 but accessed with 240x67 dimensions. Fix this by checking whether the console dimensions changed while in the alternate screen. If they did, free the stale saved buffer instead of restoring it. The unicode screen will be lazily rebuilt via vc_uniscr_check() when next needed.

Weaknesses 1

Affected Products 4

References 3

• git.kernel.org https://git.kernel.org/stable/c/40014493cece72a0be5672cd86763e53fb3ec613
  Patch
• git.kernel.org https://git.kernel.org/stable/c/428fdf55301e6c8fa5a36b426240797b1cf86570
  Patch
• git.kernel.org https://git.kernel.org/stable/c/891d790fdb5c96c6e1d2841e06ee6c360f2d1288
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/40014493cece72a0be5672cd86763e53fb3ec613
  Patch
• git.kernel.org https://git.kernel.org/stable/c/428fdf55301e6c8fa5a36b426240797b1cf86570
  Patch
• git.kernel.org https://git.kernel.org/stable/c/891d790fdb5c96c6e1d2841e06ee6c360f2d1288
  Patch