From: Maciej W. Rozycki macro@orcam.me.uk
commit 860dafa902595fb5f1d23bbcce1215188c3341e6 upstream.
Restore the original intent of the VT_RESIZEX ioctl's `v_clin' parameter which is the number of pixel rows per character (cell) rather than the height of the font used.
For framebuffer devices the two values are always the same, because the former is inferred from the latter one. For VGA used as a true text mode device these two parameters are independent from each other: the number of pixel rows per character is set in the CRT controller, while font height is in fact hardwired to 32 pixel rows and fonts of heights below that value are handled by padding their data with blanks when loaded to hardware for use by the character generator. One can change the setting in the CRT controller and it will update the screen contents accordingly regardless of the font loaded.
The `v_clin' parameter is used by the `vgacon' driver to set the height of the character cell and then the cursor position within. Make the parameter explicit then, by defining a new `vc_cell_height' struct member of `vc_data', set it instead of `vc_font.height' from `v_clin' in the VT_RESIZEX ioctl, and then use it throughout the `vgacon' driver except where actual font data is accessed which as noted above is independent from the CRTC setting.
This way the framebuffer console driver is free to ignore the `v_clin' parameter as irrelevant, as it always should have, avoiding any issues attempts to give the parameter a meaning there could have caused, such as one that has led to commit 988d0763361b ("vt_ioctl: make VT_RESIZEX behave like VT_RESIZE"):
"syzbot is reporting UAF/OOB read at bit_putcs()/soft_cursor() [1][2], for vt_resizex() from ioctl(VT_RESIZEX) allows setting font height larger than actual font height calculated by con_font_set() from ioctl(PIO_FONT). Since fbcon_set_font() from con_font_set() allocates minimal amount of memory based on actual font height calculated by con_font_set(), use of vt_resizex() can cause UAF/OOB read for font data."
The problem first appeared around Linux 2.5.66 which predates our repo history, but the origin could be identified with the old MIPS/Linux repo also at: git://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git as commit 9736a3546de7 ("Merge with Linux 2.5.66."), where VT_RESIZEX code in `vt_ioctl' was updated as follows:
if (clin) - video_font_height = clin; + vc->vc_font.height = clin;
making the parameter apply to framebuffer devices as well, perhaps due to the use of "font" in the name of the original `video_font_height' variable. Use "cell" in the new struct member then to avoid ambiguity.
[1] https://syzkaller.appspot.com/bug?id=32577e96d88447ded2d3b76d71254fb85524583... [2] https://syzkaller.appspot.com/bug?id=6b8355d27b2b94fb5cedf4655e3a59162d9e48e...
Signed-off-by: Maciej W. Rozycki macro@orcam.me.uk Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org # v2.6.12+ Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/vt/vt_ioctl.c | 6 ++--- drivers/video/console/vgacon.c | 44 ++++++++++++++++++++--------------------- include/linux/console_struct.h | 1 3 files changed, 26 insertions(+), 25 deletions(-)
--- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -895,17 +895,17 @@ int vt_ioctl(struct tty_struct *tty, if (vcp) { int ret; int save_scan_lines = vcp->vc_scan_lines; - int save_font_height = vcp->vc_font.height; + int save_cell_height = vcp->vc_cell_height;
if (v.v_vlin) vcp->vc_scan_lines = v.v_vlin; if (v.v_clin) - vcp->vc_font.height = v.v_clin; + vcp->vc_cell_height = v.v_clin; vcp->vc_resize_user = 1; ret = vc_resize(vcp, v.v_cols, v.v_rows); if (ret) { vcp->vc_scan_lines = save_scan_lines; - vcp->vc_font.height = save_font_height; + vcp->vc_cell_height = save_cell_height; console_unlock(); return ret; } --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -379,7 +379,7 @@ static void vgacon_init(struct vc_data * vc_resize(c, vga_video_num_columns, vga_video_num_lines);
c->vc_scan_lines = vga_scan_lines; - c->vc_font.height = vga_video_font_height; + c->vc_font.height = c->vc_cell_height = vga_video_font_height; c->vc_complement_mask = 0x7700; if (vga_512_chars) c->vc_hi_font_mask = 0x0800; @@ -512,32 +512,32 @@ static void vgacon_cursor(struct vc_data switch (c->vc_cursor_type & 0x0f) { case CUR_UNDERLINE: vgacon_set_cursor_size(c->vc_x, - c->vc_font.height - - (c->vc_font.height < + c->vc_cell_height - + (c->vc_cell_height < 10 ? 2 : 3), - c->vc_font.height - - (c->vc_font.height < + c->vc_cell_height - + (c->vc_cell_height < 10 ? 1 : 2)); break; case CUR_TWO_THIRDS: vgacon_set_cursor_size(c->vc_x, - c->vc_font.height / 3, - c->vc_font.height - - (c->vc_font.height < + c->vc_cell_height / 3, + c->vc_cell_height - + (c->vc_cell_height < 10 ? 1 : 2)); break; case CUR_LOWER_THIRD: vgacon_set_cursor_size(c->vc_x, - (c->vc_font.height * 2) / 3, - c->vc_font.height - - (c->vc_font.height < + (c->vc_cell_height * 2) / 3, + c->vc_cell_height - + (c->vc_cell_height < 10 ? 1 : 2)); break; case CUR_LOWER_HALF: vgacon_set_cursor_size(c->vc_x, - c->vc_font.height / 2, - c->vc_font.height - - (c->vc_font.height < + c->vc_cell_height / 2, + c->vc_cell_height - + (c->vc_cell_height < 10 ? 1 : 2)); break; case CUR_NONE: @@ -548,7 +548,7 @@ static void vgacon_cursor(struct vc_data break; default: vgacon_set_cursor_size(c->vc_x, 1, - c->vc_font.height); + c->vc_cell_height); break; } break; @@ -559,13 +559,13 @@ static int vgacon_doresize(struct vc_dat unsigned int width, unsigned int height) { unsigned long flags; - unsigned int scanlines = height * c->vc_font.height; + unsigned int scanlines = height * c->vc_cell_height; u8 scanlines_lo = 0, r7 = 0, vsync_end = 0, mode, max_scan;
raw_spin_lock_irqsave(&vga_lock, flags);
vgacon_xres = width * VGA_FONTWIDTH; - vgacon_yres = height * c->vc_font.height; + vgacon_yres = height * c->vc_cell_height; if (vga_video_type >= VIDEO_TYPE_VGAC) { outb_p(VGA_CRTC_MAX_SCAN, vga_video_port_reg); max_scan = inb_p(vga_video_port_val); @@ -620,9 +620,9 @@ static int vgacon_doresize(struct vc_dat static int vgacon_switch(struct vc_data *c) { int x = c->vc_cols * VGA_FONTWIDTH; - int y = c->vc_rows * c->vc_font.height; + int y = c->vc_rows * c->vc_cell_height; int rows = screen_info.orig_video_lines * vga_default_font_height/ - c->vc_font.height; + c->vc_cell_height; /* * We need to save screen size here as it's the only way * we can spot the screen has been resized and we need to @@ -1053,7 +1053,7 @@ static int vgacon_adjust_height(struct v cursor_size_lastto = 0; c->vc_sw->con_cursor(c, CM_DRAW); } - c->vc_font.height = fontheight; + c->vc_font.height = c->vc_cell_height = fontheight; vc_resize(c, 0, rows); /* Adjust console size */ } } @@ -1107,12 +1107,12 @@ static int vgacon_resize(struct vc_data */ screen_info.orig_video_cols = width; screen_info.orig_video_lines = height; - vga_default_font_height = c->vc_font.height; + vga_default_font_height = c->vc_cell_height; return 0; } if (width % 2 || width > screen_info.orig_video_cols || height > (screen_info.orig_video_lines * vga_default_font_height)/ - c->vc_font.height) + c->vc_cell_height) return -EINVAL;
if (con_is_visible(c) && !vga_is_gfx) /* who knows */ --- a/include/linux/console_struct.h +++ b/include/linux/console_struct.h @@ -62,6 +62,7 @@ struct vc_data { unsigned int vc_rows; unsigned int vc_size_row; /* Bytes per row */ unsigned int vc_scan_lines; /* # of scan lines */ + unsigned int vc_cell_height; /* CRTC character cell height */ unsigned long vc_origin; /* [!] Start of real screen */ unsigned long vc_scr_end; /* [!] End of real screen */ unsigned long vc_visible_origin; /* [!] Top of visible window */