sixel, stbi, sandbox: fix fstat sandbox violation

Until recently, glibc used to implement it as fstatat. So don't trap
for fstatat (and for consistency, fstat), but return EPERM.

Just to be sure, rewrite sixel & stbi to never call fread.

1 files changed, 40 insertions, 47 deletions

diff --git a/adapter/img/sixel.nim b/adapter/img/sixel.nim
index d34f8cf8..7f2cdb5d 100644
--- a/adapter/img/sixel.nim
+++ b/adapter/img/sixel.nim
@@ -20,26 +20,17 @@ import std/os
 import std/posix
 import std/strutils
 
+import io/dynstream
 import types/color
 import utils/sandbox
 import utils/twtstr
 
-const STDOUT_FILENO = 1
-
-proc writeAll(data: pointer; size: int) =
-  var n = 0
-  while n < size:
-    let i = write(STDOUT_FILENO, addr cast[ptr UncheckedArray[uint8]](data)[n],
-      int(size) - n)
-    assert i >= 0
-    n += i
-
-proc puts(s: string) =
-  if s.len > 0:
-    writeAll(unsafeAddr s[0], s.len)
+proc puts(os: PosixStream; s: string) =
+  os.sendDataLoop(s)
 
 proc die(s: string) {.noreturn.} =
-  puts(s)
+  let os = newPosixStream(STDOUT_FILENO)
+  os.puts(s)
   quit(1)
 
 const DCSSTART = "\eP"
@@ -147,18 +138,15 @@ proc trim(trimMap: var TrimMap; K: var int) =
   node.n = n
   K = k
 
-proc getPixel(s: string; m: int; bgcolor: ARGBColor): RGBColor {.inline.} =
-  let r = uint8(s[m])
-  let g = uint8(s[m + 1])
-  let b = uint8(s[m + 2])
-  let a = uint8(s[m + 3])
-  var c0 = RGBAColorBE(r: r, g: g, b: b, a: a)
+proc getPixel(img: seq[RGBAColorBE]; m: int; bgcolor: ARGBColor): RGBColor
+    {.inline.} =
+  var c0 = img[m]
   if c0.a != 255:
     let c1 = bgcolor.blend(c0)
     return RGBColor(uint32(rgb(c1.r, c1.g, c1.b)).fastmul(100))
   return RGBColor(uint32(rgb(c0.r, c0.g, c0.b)).fastmul(100))
 
-proc quantize(s: string; bgcolor: ARGBColor; palette: int): Node =
+proc quantize(img: seq[RGBAColorBE]; bgcolor: ARGBColor; palette: int): Node =
   let root = Node(leaf: false)
   # number of leaves
   var K = 0
@@ -168,9 +156,8 @@ proc quantize(s: string; bgcolor: ARGBColor; palette: int): Node =
   # batch together insertions of color runs
   var pc0 = RGBColor(0)
   var pcs = 0u32
-  for i in 0 ..< s.len div 4:
-    let m = i * 4
-    let c0 = s.getPixel(m, bgcolor)
+  for m in 0 ..< img.len:
+    let c0 = img.getPixel(m, bgcolor)
     if pc0 != c0:
       if pcs > 0:
         K += int(root.insert(pc0, trimMap, n = pcs))
@@ -347,13 +334,13 @@ proc createBands(bands: var seq[SixelBand]; chunkMap: seq[SixelChunk];
     if not found:
       bands.add(@[unsafeAddr chunk])
 
-proc encode(s: string; width, height, offx, offy, cropw: int; halfdump: bool;
-    bgcolor: ARGBColor; palette: int) =
+proc encode(img: seq[RGBAColorBE]; width, height, offx, offy, cropw: int;
+    halfdump: bool; bgcolor: ARGBColor; palette: int) =
   # reserve one entry for transparency
   # (this is necessary so that cropping works properly when the last
   # sixel would not fit on the screen, and also for images with !(height % 6).)
   let palette = palette - 1
-  let node = s.quantize(bgcolor, palette)
+  let node = img.quantize(bgcolor, palette)
   # prelude
   var outs = "Cha-Image-Dimensions: " & $width & 'x' & $height & "\n\n"
   let preludeLenPos = outs.len
@@ -368,13 +355,13 @@ proc encode(s: string; width, height, offx, offy, cropw: int; halfdump: bool;
     # prepend prelude size
     let L = outs.len - 4 - preludeLenPos # subtract length field
     outs.setU32BE(uint32(L), preludeLenPos)
-  puts(outs)
-  let W = width * 4
+  let os = newPosixStream(STDOUT_FILENO)
+  let W = width
   let H = W * height
   let realw = cropw - offx
   var n = offy * W
   var ymap = ""
-  var totalLen = 0
+  var totalLen = 0u32
   # add +2 so we don't have to bounds check
   var dither = Dither(
     d1: newSeq[DitherDiff](realw + 2),
@@ -382,17 +369,19 @@ proc encode(s: string; width, height, offx, offy, cropw: int; halfdump: bool;
   )
   var chunkMap = newSeq[SixelChunk](palette)
   var nrow = 1
+  # buffer to 64k, just because.
+  const MaxBuffer = 65546
   while true:
     if halfdump:
-      ymap.putU32BE(uint32(totalLen))
+      ymap.putU32BE(totalLen)
     for i in 0 ..< 6:
       if n >= H:
         break
       let mask = 1u8 shl i
       var chunk: ptr SixelChunk = nil
       for j in 0 ..< realw:
-        let m = n + (offx + j) * 4
-        let c0 = s.getPixel(m, bgcolor).correctDither(j, dither)
+        let m = n + offx + j
+        let c0 = img.getPixel(m, bgcolor).correctDither(j, dither)
         var diff: DitherDiff
         let c = node.getColor(c0, nodes, diff)
         dither.fs(j, diff)
@@ -424,27 +413,27 @@ proc encode(s: string; width, height, offx, offy, cropw: int; halfdump: bool;
       zeroMem(addr dither.d2[0], dither.d2.len * sizeof(dither.d2[0]))
     var bands: seq[SixelBand] = @[]
     bands.createBands(chunkMap, nrow)
-    outs.setLen(0)
-    for band in bands:
-      if outs.len > 0:
+    let olen = outs.len
+    for i in 0 ..< bands.len:
+      if i > 0:
         outs &= '$'
-      outs.compressSixel(band)
+      outs.compressSixel(bands[i])
     if n >= H:
       outs &= ST
-      totalLen += outs.len
+      totalLen += uint32(outs.len - olen)
       break
     else:
       outs &= '-'
-      totalLen += outs.len
-      puts(outs)
+      totalLen += uint32(outs.len - olen)
+      if outs.len >= MaxBuffer:
+        os.sendDataLoop(outs)
+        outs.setLen(0)
     inc nrow
   if halfdump:
-    ymap.putU32BE(uint32(totalLen))
+    ymap.putU32BE(totalLen)
     ymap.putU32BE(uint32(ymap.len))
     outs &= ymap
-    puts(outs)
-  else:
-    puts(outs)
+  os.sendDataLoop(outs)
 
 proc parseDimensions(s: string): (int, int) =
   let s = s.split('x')
@@ -512,9 +501,13 @@ proc main() =
       else:
         palette = 1024
     if width == 0 or height == 0:
-      puts("Cha-Image-Dimensions: 0x0\n")
+      let os = newPosixStream(STDOUT_FILENO)
+      os.sendDataLoop("Cha-Image-Dimensions: 0x0\n")
       quit(0) # done...
-    let s = stdin.readAll()
-    s.encode(width, height, offx, offy, cropw, halfdump, bgcolor, palette)
+    let n = width * height
+    var img = cast[seq[RGBAColorBE]](newSeqUninitialized[uint32](n))
+    let ps = newPosixStream(STDIN_FILENO)
+    ps.recvDataLoop(addr img[0], n * 4)
+    img.encode(width, height, offx, offy, cropw, halfdump, bgcolor, palette)
 
 main()